How to bleed Yamaha trim system after changing motor?

I changed the trim motor on a 1998 Yamaha 225 hp saltwater series. The new trim motor works but doesn't lift the weight of the motor. If you put it up manually, lock it in and operate the switch, you can watch the two smaller pistons work, but they won't if the weight of the engine is on them. Through research it seems like I have a ton of air trapped in the system, but I can't seem to bleed it out. It is also quite heavy to lift up and down, so I'm trying to find the best way to bleed it. Any help is appreciated