How do I delete some but not every photo i've synced via finder

The photos on my iPhone take up a significant chunk of space and theres some that I want to delete. The problem is I've had to factory reset my phone in the past due to some personal matters but beforehand i imported all my photos and videos onto my mac. I synced all those photos back to my phone after the reset but not i'm barley able to do much with them in the photos app. Not only that but I cant even delete them. All the solutions say to sync again and delete them but that deletes every photo that has ever been synced and i don't want to delete some of them.