The process for changing one’s name and/or gender on a driver’s license or state identification varies from state to state.
In California, name change and/or gender marker change on a CA License or state ID does not require a doctor's letter. The gender marker category options are now male, female, or non-binary. To update your ID, go to your local DMV in-person and bring you current ID, your payment, your court order, and a completed DL-329S. You can also complete the DL-44 online to speed up the process, but it's not required to be completed beforehand. A court order, while not required, will help the process go more smoothly, and will prevent any issues with mis-matched documents down the line.
For a gender marker change in other states, most require that a health care provider fill out a form and/or write a letter, but different language is required for different states. They will require the originals of the form and/or letter. To learn about the requirements in your state, visit the National Center for Transgender Equality’s Interactive Map.