I recently purchased Deco AX 3000 X55 with 3 routers. They are working fine. However, I brought an additional set of Deco AX 3000 X55 with 3 additional routers. When I try to connect using the app, it will not let me. However, I am able to setup a a whole new network which I do not want. I tried resetting the new routers but cannot seem to add it to the existing network. 

Any suggestions on how can I connect the additional 3 to the same network?