Replaced Charging Port after water damage, now not getting service

Hey I have an Iphone 5s and I replaced my charging port because the headphone jack connected to it was messed up because of water damage that happened months ago, shortly after receiving my phone back I encountered the problem of at most only getting two bars of 4G service in places where I usually have 5 bars of LTE, the phone repair place replaced both cellular attenas but I am still having the same problem I saw on an old post that they had the same problem as me once they replaced the charging port and they just cleaned the antenna screw and adjusted it and their problem was fixed, is that what I need to do and if so how do I do that I have never opened up my phone before but don't want to get a new phone seeing as I just paid to have a repair done.