Item not received after marked delivered

Hello. I sold an item and right away the buyer asked me to send the item to a different address in the same city as eBay given address. I told them I could only sent it to the address eBay gave me. They said ok.

The item gets delivered but two days later, the buyer opens a case saying the item was not received. The message they sent when opening the case says, “I know it says delivered but it was not there.”

eBay says we can ask them to step in on the 4th which is today but I cannot find an option to ask eBay for help. All it says is waiting for buyer to respond. How would I ask eBay for help to get this situated?

Thank you in advance.