I need help. how to put the roller to work with the cassette (change power shift to change whatts)
Are you riding the wahoo Rollr? Or just regular rollers?
In order for watts to change something needs to be connected to SYSTM. It could be a power meter or it could be a speed sensor but you need something. Then you can use virtual watts.
I was doing that for awhile on Elite dumb rollers.
my role is wahoo kickr core
If you want to change power by changing gears on the Kickr Core, then what you want to do is use Level Mode, instead of ERG mode.
If you are riding SYSTM, here is a link to show you the difference and how to do it.