XF 2.1 How to change Media Gallery Thumbnail

[AtomicZombie]

I am enjoying my new XFMG, and would like to change one thing... the thumbnail of the album.
Seems I would have to do this at the database level.

Does anyone know where in the database these are stored?

Here is the url for one example...

https://atomiczombie.com/forum/data/xfmg/album_thumbnail/0/27-807391a7a4cee773f86d8dbed8112b10.jpg?1550966868

I should be able to just find the url of the thumbnail I want to use and switch them.
At least, that's my guess so far.

Thanks,
Brad