If you know, tell me how to set up old routers.

As long as the secondary router has wds function, you can see if tp has wds function and let him be the secondary router. The settings are all on the secondary route. You only need to know some data about the main route. The general process is to open the secondary route using wds, scan the main route, enter the account password of the main route, then set the IP of the secondary route, and close the secondary route. dhcp. See the tutorial for detailed instructions.