If an observation is associated with a project, I can go to the Observation page in the website, and click on the gear next to the project. That gives me a menu with a few options, including “Edit Global Project Settings”. That option links to https://www.inaturalist.org/users/edit#projects:
… but since the recent rearrangement of the Account Settings page, the global project settings seem to actually live over at https://www.inaturalist.org/users/edit#content:
