I've my oil pressure indicator light constantly on after I replaced the transmission

So I realised dat dis is d only place I can get professional solution to my vehicle problems wit the incompetent mechanics we have here. So I just change d transmission of my 2007 xterra after being a victim of d nissan transmission faliure, d transmission work beautifully wEll but since d replacement, wen I start d car, d oil pressure indicator light stays on as well as d service engine soon light on. I ran a scan on it and got d code p0710, can any1 pls tell me were dis sensor is and how I can identify it. A picture showing where it is would be really appreciated. Another thing, doing d time d transmission was been replaced d cam sensor one way or the other got missing, d mechanic told me so, so dat was replaced also, could dis cause d problem, probably it wasn't d right sensor, but d engine start. Thanks