let's start with the basics first in order to solve your tablet issue. Once we go that, we can move forward as necessary.
I would recommend performing an antivirus scan on your device. You can search for "avast" or "malwarbytes" in your app store to get started.
If that doesn't work, then you can perform a factory reset as described by Samsung here: https://www.samsung.com/us/support/answer/ANS00062842/
. You'll be advised to back up your files before performing the factory reset.
Please let me know if this helped you or not.