Before getting started, please note that customisation only applies to native stores, as opposed to the web store.
Learn more about the differences between web store and native store.
🎨 Go the Settings / Customisation section of your store
There, you can change your store name and add an icon that will appear on your users devices.

You can also change the colours of your store.
A message will warn you if we detect that the contrasts between the text colour and the background colour is low

Once you're done, hit the "Save changes" button in the upper right corner.
⚠️Rebuild your store for changes to apply!
You probably want those changes to apply for your users, right ? Then there's one last thing to do !
Go to the "Native stores and updates" section
click on the "Build iOS store" or "Build Android Store" button:

This will generate a new version of your store and send a push notification to your users. Next time your users open their store, it will update automatically and they will benefit from the customisation.