The left side of the skull was smashed out of a depression, indicating that a depressed fracture of the skull occurred at that time. If there was no surgical reduction at that time, it would have become bone healing by now. You can't go back to your original state unless you have another operation, but I'm afraid no hospital or doctor will do it for you (meaningless and risky).

Another possibility is that you had an operation (you didn't explain the treatment process at that time) and removed a small piece of skull when you opened the skull. What I feel now is this defect. In this case, if necessary, surgical repair can be performed.