Use airport express to extend a bridged network
I recently had google fiber hooked up at my house. Previously I had AT&T. With AT&T I had a time capsule and an airport express. I turned the wireless off from AT&T and was using the time capsule as my primary wireless and was extending the network with the airport express. The way that google set up the wireless was they are using two bridged networks in my house now. One uses the google router and the other uses the time capsule. Is it possible and if so how do I go about setting up the airport express to extend the network that the time capsule is using which is being bridged with the google router. I know that I have done this before but I don't remember how at this point and just plugging the air port express back into the wall does not work, in fact, it causes the network created by the timecapsule to crash completely when I just plug it back into the wall so I figured I needed to start over with the set up. It was explained to me before and I remember it being simple but that the order in which it was done was critical.
Thank you in advance for your help