How does one go about doing this??

For starts, have you tried our NFA forum?

Fixed that for you 

Do you have a SBR and a Silencer or is it a permanently attached 22 silencer? More details are definitely better so we can actually figure out what you have.

Why sell? And the buyer still pays another $200 even if a dealer buys it. The rifle can just have a long barrel added and keep it or sell it, its no longer nfa.

You're screwed if you want to sell them.
The buyer would be paying $400 for each transfer. So if he bought the SBR and the can it would cost him $800. The recipient of a NFA item owes the $200 tax regardless if the recipient is a dealer or individual (dealer, manufacturer, or LE agency to a dealer is different), and that dealer will pass that on to their customer. Plus it will likely be the full 8 plus months for the transfer to the dealer so the person buying it will be waiting a year and a half.
As stupid as it is the way RCW 9.41.113 is worded it has to go through a dealer. Even if you just had a fingerprint based background check done on you by the ATF.

No dealer will buy them from you unless you're going to pay the tax on each item and that will likely not even make it worth selling. Same with a consignment since to be able to transfer it, the dealer has to take possession of it, meaning that dealer has to pay the tax.

The temporary transfer to a dealer for a repair is an exception.

There is a technicality here that can be exploited. Technically, the lower receiver by itself is just a receiver and can be transferred as such. You could fill out the form 4 transfer between the two parties and then once the stamp comes back, you could just transfer the lower through a shop.

Doesn't work for the suppressor, but as it isn't a firearm, it does not have to go through a shop.

So in total, would be $400

Suppressors are firearms!

26 U.S. Code § 5845 - Definitions

For the purpose of this chapter—
(a) Firearm
The term “firearm” means (1) a shotgun having a barrel or barrels of less than 18 inches in length; (2) a weapon made from a shotgun if such weapon as modified has an overall length of less than 26 inches or a barrel or barrels of less than 18 inches in length; (3) a rifle having a barrel or barrels of less than 16 inches in length; (4) a weapon made from a rifle if such weapon as modified has an overall length of less than 26 inches or a barrel or barrels of less than 16 inches in length; (5) any other weapon, as defined in subsection (e); (6) a machinegun; (7) any silencer (as defined in section 921 of title 18, United States Code); and (8) a destructive device. The term “firearm” shall not include an antique firearm or any device (other than a machinegun or destructive device) which, although designed as a weapon, the Secretary finds by reason of the date of its manufacture, value, design, and other characteristics is primarily a collector’s item and is not likely to be used as a weapon.

And if he sold them out of state it could be $800 in tax for his used old stuff with possibly his name and location scratched on the side if they are off of a Form1.  So generally not worth it unless it is a historic firearm; if it is an AR lower that you can get for $50 there is no point.

True, if he sold them out of state they would have to go through a dealer, but in state, silencers can just change hands once the approved form 4 is returned.

Not quite. Not unless he first took the SBR off of the NFA Registry. If he doesn't, then regardless of it's current configuration it still must be transferred as a SBR. It's not a receiver, it's a SBR in what hte ATF calls a "knockdown state."

Once the defining feature is removed, which would be the upper receiver, the remaining portions do not retain their NFA status. Once the form 4, between seller and buyer, is approved for the transfer, you and the buyer go to a shop and transfer the lower as just a lower. You could even throw on a 16" upper and transfer it as a rifle through a shop if it made you feel better.

NFA Handbook - Chapter 2 - Section 2.5

You're right. It's still registered, but if not in a SBR state, it's not an SBR at that moment. You can send a letter to the NFA branch stating it's no longer a title 2 firearm, but apparently there is no legal or regulatory requirement to do so.
But if you have all the parts to make an SBR in "close proximity" with no other purpose but to make a SBR the ATF considers you to have a SBR. Some odd logic there.