In Photos on Mac, click Bursts under Albums [sidebar] to locate the burst photos.
Double-click the photo you want to un-burst.
The main photo will appear with Make a Selection button in the upper left corner. Click this.
You are now on the Make a Selection screen, which will show how many photos are in the burst. At the bottom is a thumbnail representation of each the photos.
Select one thumbnail. If you want to keep this photo - Click on the PHOTO to select it. A checkmark will appear on the bottom right of the photo.
Continue the process, selecting each thumbnail in turn and deciding to separate the photo or not by clicking on the ones you want to keep.
When you are done, click Done in upper right corner.
If you have selected all of the individual photos, the burst item will disappear from the Bursts grouping, and they will become individual photos.
If you do not want the remaining photos - if any - in the original burst, then delete it and you have removed it from your devices.
HTH,
Michele