From your PC, please right-click any area in the "Market Watch" view and select "Show All" to view all symbols. You can click "Symbols" to add/hide symbols individually.

From your mobile device, please open your app and press the "+" icon from the upper right-hand corner to add a symbol.

To remove a symbol:
For Android, you can do so by pressing the "pencil" icon in the upper right-hand corner > "product" > "trash can" icon.
For iOS, you can do so by pressing the "pencil" icon in the left upper right-hand corner > "product" > "trash can" icon.