Hi and Welcome
1. Charge your tablet
2. Turn it ON
3. Log into your Samsung account on PC ( if you are using the same account on all devices) and maybe see if you can RESET tit from there.
3a. While there, if you could REMOTE UNLOCK under FIND ME mobile if you had set it up.
4. If you had done a backup before you stopped using it, then you may be able to get everything back when you sign in again by restoring from backup
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