ChatGPT doesn't remember a character between separate conversations. The fix is giving it the same reference every time, not hoping it recalls.
Give it a reference to work from
Upload one clear reference image of the character and keep reusing that exact same upload for every new image.
Describe the fixed details every time too: hair color, outfit, build. Don't assume the model remembers them from your last message.
Ask it to edit the existing image rather than generate a new one when the change is small, like a different pose or background.
Lock down the details that tend to drift
Clothing color and hairstyle are the two things most likely to shift between generations. Restate both explicitly each time.
Say "preserve facial features exactly as in the uploaded photo" directly in your prompt. It is a real instruction, not filler.
If a generation drifts, don't keep pushing forward. Go back to the last version that looked right and edit from there instead.
Consistency isn't a setting you turn on. It's just discipline about which image you build the next one from.