To customize your Mobile App, go to "Site" > "Mobile App" > "Branding".

Within this section, you have the option to 'Add Logo' to the mobile app interface; kindly ensure that your logo is in a square format and measures 150 x 150 in size.

You can also change the 'App Theme Color' or enter your own custom hex number here.

When you're finished with branding, simply click 'Save'.

Afterward, just check your mobile app, and you'll see the changes there.