Need rdns for IPv6 block. Static changed with recent modem install

I had an rDNS delegation for the first /64 in my old ipv6 block of statics.  That /56 block changed with a modem upgrade to support newer service.

that rDNS delegation is still active.  I know longer control that /64, so that delegation should be removed.

I'd like to get the same rDNS for the initial /64 block as well as an rDNS for one specific additional /64.