How to delete synced photos/videos??

Hi All - I have an iphone 12 and there is a section in MY PHOTOS showing 3 folders "FROM MY MAC". These contain photos and some large videos (about 8gb total) that i cannot delete. The trash can button is just not available on any of these items.

My storage space is now full and i have removed most items that i can to a cloud service. I dont want to get more cloud space as i just want to get this 8gb available again.

The 3 folders are from files that i had synced from an old laptop going back to iphone 6 days. The current laptop does not have the check box ticked to sync photos. However I assume the old laptop still has this setting. This old laptop is extremely slow/temperamental. When i tried connecting the iphone to the old laptop, a message appeared stating it was incompatible and did i want to reset to factory settings, which i did not, i just unplugged.

So the real question is how can i delete these 3 folders please?

many thanks for future answers (please keep it simple as i'm not technical)

Martin