hello sir I want to partipet in uno tonomennt so kindly help regarding this thanks

Too late, for sure. Wait for the next one.

There is no specific way to join a tournament. They are posted on the tournaments forum when they happen and detail their rules. You usually just answer to the topic when you want to participate. Note however that they aren't hosted by Playroom staff so players take the responsibility themselves. At the moment, there is an active uno league that already has participants. Watch the forums for the future tournaments!