No cellular signal p30 pro

Hi I need help please, I have no cellular service but I can if I'm close to a mast, i think I may of had some water damage that's effecting this, I'm a confident person and want to try fix this my self, I have opened back and can't see no visual water any wear so I'm trying to pin point what needs replacing, so it's either the white antenna coax or the little corner piece that the coax connects to, any suggestions would be greatly appreciated