How to Purge a DNS entry router DNS CR1000A. Two entries for same IP address

[dggerman]

I have a router with 2 entries for the same IP address

Davids-MBP-4  192.168.1.30  DHCP

EasyLiz   192.168.1.30  DHCP

Davids-MBP-4 is very old

when I  issue  host  or   dig -x  Davids-MBP-4 is reported!

How do I purge Davids-MBP-4?

PS

admin page for DNS says:

 Add, edit, or delete computers known by the router's DNS server

But there does not seem to be a way to edit ir delete an entry, only add