It's a Wonderful Life (1946)
George Bailey prays to an angel (Clarence) and God to bring him his old life back, after witnessing the world that could have been if he never existed: Clarence! Clarence! Help me, Clarence! Get me ba…
Thanks to RbDeraj, peaspot, alioth4, DoctorBuster, jalapenoman and Banjo_oz for some of the suggestions