How to remove a duplicate MAC address on the router

Hello,

I mistakenly made two entries with the same MAC address as Reserved IPs. 192.168.0.99 is reserved, and 192.168.0.78 is the DHCP. I need to remove the 99 entry but is is offline since the 78 is taking its place. I don't see a way to remove the offline devices from the router or in the app. Help!