I presume you got a new castle nut with your new collapsible.
If you do not care about the old non-collabsible, you can use a big ole pipe wrench and get the old castle nut off.
Do the standard installation drill of the new collapsible.
The single pin wrench can tighten the new castle nut down sufficiently until you get the right wrench.
When you do get the right wrench, tighten down with just a bit of BLUE loctite.
edited dumb mistakes