If the bogie sideframe is quite flexible, this can happen. I clean all the oil from the axle and clean the frame socket where it sets in. Then try bending the sideframe inward. Not much else can be done.

A good idea so as the bogie can be removed easily. Some have pickup shoes, and wiring, or axle contacts.
Is the plastic going to retain the new taughtness upon cooling?

A heat gun is too fierce to use on this, the plastic will just melt.

The hot water trick is the way to go, but do it without the wheel in place. Use something such as a small cable tie to pull the bearing points in about the right amount, then duck the lot in some very hot water for about half a minute, pull it out and leave to cool. After it has cooled for a half hour or so take the cable tie off and fit the wheels.