League Cooldown: This is a very common cooldown. If you leave a league, especially while a League Tournament is active, you will be put on a cooldown period. During this time, you cannot join a new league. This is a measure to prevent players from jumping between leagues to gain an unfair advantage or disrupt tournaments. The cooldown usually lasts for a specific duration, such as 24 hours.
You better be patient for a whole day. If it's still not working try to force stop, clear cach, remove game and install it again, power off your phone, and turn it on again, clean your device and make sure that there is no problem on your device like a dangerous file or application, make sure that the storage is not full, if it's still not working try to join create a League by Yourself.