@Raziye Chamanpara -

after rejoining the team as a viewer, I'm unable to edit the board

If you are unable to edit the board, then you are not the board owner. Only the board owner can delete it, so will need to ask the new board owner to either delete the boards, or transfer ownership of the boards to you, so you can delete them.

@Robert Johnson Thanks for getting back to me.

My main issue is figuring out who's currently in charge of the board. When I tried to check the “Board details” by clicking those three dots, I didn't see the option to do so (see Image 1). 

Interestingly, I noticed that in other boards, the 'Board details' option is available, but it's missing in this particular board (see Image 2).

Without knowing who's the board owner now, I'm kind of stuck. Any ideas on how to sort this out would be awesome.

Image1:

@Raziye Chamanpara - Rather fascinating that the Board details option is hidden for a Free Plan team member. Another way to get to that info screen is by opening the board and clicking on the board title, but I see they are still obscuring the board owner.

I think you’re only option is to switch your dashboard view to list view:

Then, if you want to see the users email address, click here:

Hey @Robert Johnson 
 

Thanks for your solution! It worked perfectly.

Best,
Razi

@Raziye Chamanpara - You’re welcome! And if you cannot get ownership of the boards again to delete them, another option is to ask a Team Admin to delete that user, selecting you as the new owner of their content, and then the deleted user could immediately be readded again.

Ah, OK, I’ll make sure to reach out to the board admin! Thanks again