How to reset all users preference?

This will copy one user’s saved search for all other users:

This one is a more elegant code-based solution for the same:
https://www.ciconet.it/en/soluzioni/182-predefined-searches-in-sugarcrm-ce-65-or-suitecrm.php

This is not exactly what you need, but you can get insights from that: the user preferences are base64-encoded in the same way, only they are found in the user_preferences table.