Answering my own post...
So apparently it's really easy, on the Merlin we have there is a button in the unit, attached to the door in the garage. Press it for 6 seconds and all the remote codes are wiped. Then using the unit to reprogram the remotes. Took all of 5 minutes to program the 4 remotes we still have.
Hope this is of some help is others have lost/stolen remotes in the future.
And while I'm on it the remote is missing because my 21yo Nephew went missing over the weekend, Police are now checking his last movements. All we know is he left the house with a friend (don't know who) Sunday evening and hasn't using his phone since. Hope he comes home soon.
Before some ask 'why disable his key' well first he still has a door key but we are worried something bad has happened and god knows who could have the remote now. We still hope he is fine and just doesn't want to talk after loosing his job and other things in the last few weeks but we need to be practical in case someone has those keys and knows the address.
BTW this is his FaceBook page
https://www.facebook.com/jay.best.92?pn ... en-section