Adding another wifi access point

[mnh]

I have a wifi setup with a couple of Draytek Vigor AP810's around the house and need to add another one to address a deadspot that has a network socket available. Can someone point me in the direction of where to find simple instructions on how to do this please? I managed to log into one of the existing Draytek's last night so I know the username and password. But I'm assuming it's not going to be as simple as plug and play!