Does anyone know how to switch the bell and sand dome on the lgb fred gurley
They both are attached to the boiler with screws. There is one screw for the sand dome and one for the bell and they both are reached by completely removing the boiler from the locomotive's chassis.
You can see an assembly diagram of the almost identical 23252 "Columbus" Forney locomotive here on the LGB of America website:
The diagram shows where the screws are and what you have to remove to get to them. I disassembled my 23252 locomotive right after I bought it to install an on/off switch for the smoke unit on top of the firebox. It wasn't *too* hard to disassemble. It wasn't as easy as my 2018D mogul though, that's for sure.