You can go back to another SMS app (for example Google Messages) any time: open that app and accept its "set as default" prompt, or choose it in Settings → Apps → Default apps → SMS app.
Your quarantined messages: they're kept only in 1krBlocker, not in the phone's message store, so the other app won't show them. When 1krBlocker notices it's no longer your SMS app, it offers to move them:
- Keep them in 1krBlocker: They stay here. You can move them later in Settings → Data.
- Move them: To move them, Android needs 1krBlocker to be your SMS app for a moment. Afterwards you can switch back. Their warnings stay in 1krBlocker.
Your ordinary messages are already in the phone's message store, so the other app shows them as usual.
After switching: new messages aren't checked by 1krBlocker any more, and chat features (RCS) can be turned on again in Google Messages. 1krBlocker shows "1krBlocker isn’t your SMS app, so new messages aren’t checked." until you switch back or uninstall it.
Uninstalling 1krBlocker deletes what only it holds: quarantined messages, your rules, senders and history. Move quarantined messages and export what you want to keep first (see "Exporting everything").