Plug in into your second WAP and access its default IP (192.168.0.1). From there you should be able to tell which firmware it is. UN and PW super/sp-admin.
If your main WAP acts as a Router, then you need to add it to the L2 for the WAN, i.e. give your second WAP another public IP in the subnet, otherwise, they won't be able to find each other. If you have it connected on the LAN side, then your second WAP would be behind NAT, which would not work.
You potentially could form a second unleashed network without having to add an actual router. Make that WAP just L2 Access Point. That will keep the NAT of the Route WAP "extended" through this WAP. It would not be perfect, but it will work.
Get a L3 Router and have it do all of the NATing for the network and have the WAPs as L2 Access Points.