To expand on what @Scholli said:
You have your pattern pieces fitted to your 3D form. Seamly uses formulae & the measurements off the 3D form to create pattern pieces which will fit the 3D form. Therefore, you have to “reverse-engineer” the process to identify which measurements & formulae best describe what you have already done in a way that will translate to other forms as well.
If you are only producing a very few of the article, or use standard grading, it’s probably not worth it, save as a learning experience. However, if you aim to use this design to make custom fitted garments for a number of people, it is totally worth it.
@Douglas posted a way he worked with this way back in 2017: Shift Dress Pattern
