I just had to switch to tmobile and it only has the 5g and now I cannot switch to 2.4 in order for my camera and my vacuum to work, I am somewhat tech savy but I don’t want to mess anything up, Is there any place or anyone that can help me, my camera is outside and I have to get a ladder to reach it, I am 73 years old and don’t really feel safe doing that, I don’t have anyone that can help me. What can I do..
I have T-Mobile internet and my hub/router has both bands. If yours truly doesn’t, you can connect a second WiFi router as an access point using a Ethernet connection to the T-Mobile hub, configured with your old SSID and password running just 2.4ghz.
Welcome to the Forum, @jkramer344! 
I think it’s unlikely that your new Internet service lacks support for the 2.4 GHz Wi-Fi band, and I imagine that your new gateway supports both 2.4 GHz and 5 GHz Wi-Fi at a minimum. I also wonder if you’re conflating the 5 GHz Wi-Fi band with 5G (fifth generation cellular).
If possible, setting your new gateway to use the same Wi-Fi SSID and password you were using with your old router is probably the easiest solution, because your Cam v3 and Robot Vacuum should both automatically reconnect using those same credentials if they see such a network become available again. T-Mobile should be able to walk you through that or possibly even do it for you remotely. Have you contacted their support? If they won’t do that, then sharing more details about your equipment and how you manage it might be helpful to other community members who want to provide assistance.
Make sure you’re not confusing the 5G cellular service that feeds the router with 5ghz Wifi from the router. It almost definitely supports 2.4ghz, may have to enable it, but usually both are on by default.
If you give it the same wifi name and password, the cams should reconnect automatically without having to set them all up again.