What parts should I get when replacing mobile reception antenna

Hi everyone, so I am trying to fix my lg g5’s Reception mobile signal. I tried everything such as factory resetting the phone . Pretty much everything and I’m still getting one bar to none. I can’t even make a phone call or a text because of its poor signal. I brought it to lg to get it repaired and they are charging me close to $700 to get it repaired. Of course I’m not gonna pay that much to get it repaired so I looked up some videos online on how to take it apart and that is going very well. The only thing I need a help about is what parts should I buy to replace the mobile reception signal antenna. What does it look like? Where is it located?

Thanks in advance