If you enter an incorrect wallet PIN too many times, your wallet will become disabled for a certain amount of time. This is to prevent someone from trying to guess your PIN by making many guesses. If your wallet is disabled, wait until the time shown and you will be able to enter your PIN again.
If you continue to enter the incorrect PIN, the amount of time you will have to wait in between attempts will increase. Eventually, the app will reset and you can start a new wallet.
If you have the Paper Key for your wallet, you can use it to reset your PIN by choosing the appropriate option on the lock screen.