You should contact support to see if any recovery options exist.
This thread from 2015 discussed the same situation, here’s what @theuser86 had to say in that thread:
May '15
The database is stored locally on the Tablo so if you factory reset the Tablo you will not be able to access the recordings from the Tablo.
The drive itself still has the recordings so you can plug it into a computer and save them. Except this process will require some knowledge and work on your part.