Just factory reset it, and choose the option that downloads a fresh copy of the software.

If you don’t know to much about Networks and just want something that works. I would purchase a 2 or 3 pack of Eero 6 Pros and a network switch that has enough ports for all of the Ethernet drops. You would connect the Ethernet cable from the modem to the Eero 6 pro which will now be called your gateway/router, you will then plug an Ethernet cable from the Eero Pro 6 to your network switch. You would plug all of the Ethernet drops to your switch. Then depending on the your signal coverage you would plug in the other eeros into where you have low WiFi signal. Or you could just plug your streaming devices/game consoles to the Ethernet wall ports in the rooms. If you decide you need additional Ethernet lines in the rooms you could buy a 5 port switch.

If you have coax ports look into MoCA, it’s a great way to an Ethernet hardline by the way of your already existing coax. MoCA + an access point at the far end should do the job

Check if your phones are giving your router a private/ random MAC address