What I did was: eBay -> Summary -> Orders -> Order -> More actions -> Contact seller -> Item not received
Copy/paste from eBay message:
We're sorry to hear that you didn't receive the item you purchased. Your request is open, and we've asked the seller to respond and resolve your issue by Sep 26, 2019.
If you don't hear back or can't work something out, you can ask us to step in beginning Sep 26, 2019. If that happens, we'll review your request, gather any new info we need, and make a decision within 48 hours.