New phone won't connect to the modem (wifi/internet)

[AC Question]

I bought a new phone today, an Oppo F1. It won't connect to my modem, on my modem there is an 5G at the end of one of network names, it is not showing up on my phone. I have tried adding it, it will not work. and when i try to connect to the one without the 5G at the end of the network name it just says saved but it doesn't give me any internet. PLEASE HELP!!!!