Since no one else is giving you an answer, I'll kick it off.
I'm sure someone will be along in a minute with better advice.
You might try a little gentle lapping, but be aware, you are opening headspace. If your rifle is on the loose end of the tolerance, you could easily end up with too much headspace; an out of spec rifle.
You might get away with a couple thousandths. Might not. You would need a set of gauges to know where you are at.
Lapping is usually done during/prior to barreling, the bolt is lapped in, then the headspace is set after.
Fixes are : remove the barrel, lap the lugs in, set the barrel back one thread and ream to a good headspace.
Surplus rifles were often assembled with miss matched parts by simply trying bolts until one was found that would headspace with the action.
You could try a new bolt, but it would be a crapshoot that it would be an improvement.
Finally, if you reload....You can lap until you have full contact, even if you are out of spec, then set your sizing die to just bump the shoulder on your " fireformed" cases, which will have stretched to the new, longer chamber dimensions, creating a mini-wildcat, as it were.
But you must be very careful and know your business, continually resizing the cases to original size and firing them is a recipe for case failure, bad things can happen. In addition, it would be dangerous and unethical if the rifle could ever be sold or passed on in this condition, which would essentially in " No-go" headspace condition.
Best bet: pull the barrel, lap lugs, set back barrel, recut the chamber.