All of Me (1984) on Netflix

Roger Cobb is a lawyer by day and a jazz musician at night. His boss refuses to let him to anything substantial unless he decides on what he is. When Roger says he is, his boss puts him in charge of handling the estate of Edwina Cutwater, a spoiled wealthy heiress, who tells Roger that she is dying but she has contingency plan which she wants Roger to handle. And that being she is going to leave all of her wealth to Terry Hoskins, the daughter of the groundskeeper, and she has brought a Swami from Tibet to perform a ritual wherein her soul is transferred into Terry. Roger thinks that she is being a spoiled brat, so he storms out. Later at the office the Swami is doing the ceremony when something goes wrong and Edwina enters Roger's body. Now she has control of half of his body, and all what she and Roger want is for her to get out but no one can find the Swami. And while they do, Edwina disrupts Roger's life.