There is a button on the box itself, if you press that button it re-pairs the remote with the box however if you press it and then apply power to the box (at the same time) it will do a factory reset.
This is in the flyer/instructions that comes with the newer Onn Android with Google TV but I assume it applies to the older one as well, I don’t know that for a fact.
Also, I must have gotten lost in reading the replies, I thought it had already been reset, sorry if I added confusion to the conversation.
Again good luck…