iPhone 1st gen SE cannot connect to 5G
My husband's iPhone 1st gen SE is a battery hog. It will only get 1X or 3G connections but it used to get 4G connections. Our area just launched 5G which I get on my iPhone 12, but he cannot get the 5g
connection. He has trouble connection to our home internet. I went to a local phone repair shop to ask what might be going on with the phone. They told him to back it up, erase it, and then download "something" from the internet to reinstall the iPhone operating system. (My husband isn't a techie so he didn't understand the "something" that he should download.) Can anyone tell me what should be downloaded to his phone?
Thanks.
[Re-Titled by Moderator]
iPhone SE, iOS 15