Register for Clash Royale Tournament inside MPL. Make sure that your Clash Royale player details are correct. Else, you will be not be able to play and get your rewards.
You will receive joining details for Clash Royale 60 mins before the tournament starts.
Copy or note down the Tournament ID and Password provided on tournament details page
On Clash Royale, go to Tournaments section
Search for a tournament using the tournament ID copied from MPL Pro app.
Join the tournament using the password copied from MPL Pro app.
Start playing your battles once the preparation phase ends.
Restart Clash Royale if you are unable to join the room after receiving the Room details.