There is no Tildes mobile app, and there is no plan to make an official app for Tildes.
To use Tildes on your tablet or smartphone, simply open your internet browser and navigate to https://tildes.net. The Tildes website will automatically adapt its display settings to fit your screen, whether large or small. Some browsers also allow you to create a shortcut on the device's home screen, which will take you directly to the website.
Reference: The site is the main mobile interface, not an app
You can propose changes to this page by editing the copy of it available in the wiki for the ~tildes.official group on Tildes itself.