@Ca_Gi Settings > Content > PeerTube instances. There you can add instances by pasting the URL and select the one you want to use as default.

After that, you open the menu and, right below the title of the app, you'll probably see “YouTube“. Tap on that and change to your default PeerTube instance.

È complicato, ma non impossibile. Mi dispiace, ma il mio italiano è molto povero.