Cellular Antenna Not Working, How easy to repair?

Hey guys,

Recently started having a issue with my phone no longer getting any cellular reception after replacing me screen and getting my charging port fixed as it was no longer working. My phone was working fine for a few weeks then it stopped working.

Today I took it back to a different phone shop and he opened it up and started playing with a little gold thing to the bottom right of the screen and said it was loose. It started working again but now after about 3 hours of use it has stopped again. I tapped on the back on the phone where he played with it and it came on for a breif moment but turned back off again.

I just wanted to know what needs to be repaired/replaced in order for this issue to be fixed and if anyone has a rough idea on a cost for how much it should be?

Much appreciated!!!