Do you just go to the home/feed and let it be fed to you? Do you have things you follow specifically and nothing else? Somewhere in between?
I use the web client, but it should be wherever your block list is. Webclient you have to manually type it in, there should be three sections:
Accounts
Communities
Instances
So if you can’t figure it out in your app, you can just sign on via a webpage to block instances and that should effect the app since it’s about your account and not the client.