assuming the photo has coordinates associated with it, clicking on the “Sync?” above the photo in the Edit screen on the website should set the coordinates of the observation to the photo’s coordinates. i tried it with one of my observations (https://www.inaturalist.org/observations/67714614) which i corrected the coordinates of because the photo’s coordinates are really off, and clicking “Sync?” puts the coordinates of the observation back to the bad coordinates (but i did not save the bad coordinates). the accuracy circle still reflects my manually updated accuracy value, since the photo does not have a horizontal positioning error recorded in its metadata.
do you mind sharing a link to the observation you’re trying to change?