How do I fix loose cellular antenna connection?

I discovered that my phone is stuck on searching all the time.. Occasionally there is some signal but it returns to searching after 10 to 15 minutes..! I have tried everything already including reseting the network settings, all settings, doing a hard reset, installing updates, restoring the system, trying different SIM-cards, etc.

However, I stumbled upon some suggestions that the cause might be a loose antenna after dropping the phone..! So I think the only solution is to exchange the cellular antenna or somehow repair it..? I have some experience on opening my iPhone since I changed the battery the other day... Thank you in advance for all your answers/suggestions!