help restore sub site access accidentally deleted theme on the network and now the sub-site is

I am trying to teach a high school student how to use wordpress. We created a sub-site for him to "play with " themes and customization.

I didn't realize he used a theme and deleted it from the network. We tried to re-install it but it hasn't come bask to having the dashboard or any access at all.

all we see is a white screen. I am not sure which files to search and activate.

Can you help?
the site is marked JA Journals.