I have the same question. I asked the Ai and in its reasoning tab I could see that it’s apparently not possible. This is what it said:

“The user seems to have a misunderstanding about the workflow. Figma Make allows you to:

1. Import designs FROM Figma
2. Create interactive web applications based on those designs
3. Export/save the web application code

But it doesn't save back TO Figma as an editable design file. The character sheet they've created is a functional React web application, not a Figma design.

I should clarify this for them and explain what their options actually are for preserving and working with this current version.”

But then I ran out of prompts for the day, so it never actually answered my question

Turns out you can edit, but only the CSS code, which is cumbersome to say the least