OnePlus 5 Out of Service after dropping

I recently dropped my OnePlus 5 and ever since then the phone has no network - no calls, SMS, mobile network. WiFi, BT etc. works fine. Physically, there is only a small dent on the back cover above the volume buttons, and halfway to the middle.

When I attempt to manually select a network (SIM settings, Choose a network operator), there are no results, and in About section of phone, SIM status, Signal strength i 0, and Out of Service. SIM card is recognized in both SIM slots (phone asks for PIN) but no network.

I did try restarting, airplane mode, other SIM slot, but no success, and since the network disappeared right after I picked up the phone I am positive it is a hardware issue.

My question is what is the most likely part that was damaged and how to replace it ?

Going through the replacement parts, the only thing I found was

Signal Antenna Connector Board flex cable (https://www.replacebase.co.uk/for-oneplu...) but I have no idea where this part is located after watching several teardown videos.

Any advice or help would be greately appreciated.