Desktop
You will find the tournaments you are registered in just click on “Options » My Tournaments”:
It will open up a window with your tournaments:
Mobile
You should click on the 3 strokes in the upper left corner and then click on "My Tables and Tournaments". If you see a red ball at any tables or tournaments with a number, you'll be able to check the corresponding numbers of tournaments and tables you are accessing at that time. In the case of the image below, the player is only on a table.
Next, when you click on "My Tables and Tournaments", all the tables where you are currently playing will appear. You can also view all the tournaments on which you have already registered but which haven't yet started (as you can see on the image below) .