Advice needed. A journal cap came off!

Pull the motor. If the cap is damaged you don't just put another cap back on. New bearing or not. You will need to at least remove the head to pull the piston and replace the connecting rod. You can do all that in the car but it is a turd to do. Pull the motor..........There's only one way to do this....the correct way.
toolman

I think it is a main bearing, not a rod bearing,
it sounds like you have bigger problems
the caps are machined to fit that block in that position, you cant just mix and match them, or replace them and expect it to work, also how are the threads? did you find the old bolts? are they broken or stripped?