Hi Lauren,
Thanks so much for reaching out!
Just to let you know, we are limited by our Support Policy in how much we can help with customizations, but I will try to point you in the right direction.
I’d recommend starting off by taking a look at our Themer’s Guide, which can show you which templates can be edited and copied in order to achieve the results that you are looking for.
You can copy and edit the edit-event.php template and add in another image upload field there if you’d like.
Let me know how that goes!
Thanks,
Jaime