Check the antenna bars. They might be obstructed. · If that doesn’t work, try ejecting, cleaning, and re-inserting the SIM card. · I personally don’t have 7 plus, so this is some minor textbook stuff that not everyone knows.

iPhone 7s are a pieces of shit and always have network issues. Basically the modem can become lifted off the logic board and fuck everything up. Some times resetting network settings does something, other times you’re fucked. Also try doing a ispw restore of your iPhone that might help too.

Reset phone?

I have an iphone 5 and about a week ago, it lost cellular connection and kept "searching". I did not drop the phone or anything that would cause it to stop working. I tried all of the potential fixes that apple recommends short of a factory reset. I even took it to a Verizon store and they tried a different sim card and many of the things I already tried with no luck. They pretty much told me to up-grade to solve the issue. I decided to make sure it was backed up and take the phone apart. About a year ago, I bought a battery replacement kit online, so I had the suction cup and all of the tools to take the phone apart. While the screen was removed, I unhooked the battery and the cellular antenna and then plugged them back in a few minutes later and reassembled. When I turned the phone back on, I now have cellular connection. I don't know if it would work on your phone, but it might be worth a try. It saved me from a factory reset and/or replacing the phone. Good luck!