The bad news : No matter how many times you get your Tama onto the toilet, it will never use the toilet on its own.
Tamas aren't programmed to be potty trained in that way I'm afraid.
You can only get them onto the toilet (the way lucaslover explained) or let them go on the floor...
The good news: If you get them onto the toilet in time you can fill at least one - sometimes two, Happy hearts!
Best, etc.
TamaMum