PC: Tournaments that you have registered for will appear at the top in the tournament lobby. It will be displayed in italics. It will also always appear regardless of the filters you use.
Mobile: Tournaments that you have registered for will be displayed in italics and will have a 'Registered!' tag on it. It will also always appear regardless of the filters you use. To easily view only the tournaments you have registered for, you can use Filter and untick all buy-in ranges.