Sign in at 1kr.uk, open Your data and tap Download my data (JSON). You get one file with everything your account holds: your e-mail and settings, plans, phones, your AI key (only its last four characters), Deep check counts, and any messages you donated.
Your messages never come here: they stay on your phone. The account holds your plans, phones, AI key (encrypted), Deep check counts and any messages you chose to donate.
What's not in it: your messages and notes, because they were never in your account; they stay on your phones. 1krBlocker can export its own data on the phone (see "Exporting everything"); 1krNote notes can be shared from the app.
On the same page: Delete my donated messages and Delete my account.