I think you are trying to make an image transparent? You can take a Firefly generated image into Adobe Express and use that to make the image transparent. You can take it into Adobe Express by pressing the "Share" button on the lower right and then selecting "Open in Adobe Express":
Once in Adobe Express, you can select "Remove Background":
If you need to touch up what was made transparent, you can use the "Erase" feature to erase (make transparent) part of the image or restore (remove transparency) parts of the image.
I hope this helps. Let me know if you have any problems trying this out.
If you were not asking about transparency of an image, please let us know.