I am cis, but a lot of my friends picked names similar to their birth names. Something like changing Matthew into Maddie, Rocky to Roxanne, or something similar. I have one friend who had an incredibly supportive family and she took her grandmother's name. Others kinda play around with a few names they like until they find the one that suits his or her identity.
I have ONE friend, and I know this is totally rare, but she knew she was female when she was 7, and her parents went as far as picking a new name for her. She is 28 now and still goes by that name. It's what she grew up with and she says it fits her well