How to change API call user for fetching .drone.yml
Drone uses the token of the individual that enabled the repository. To change the user account used to fetch the yaml, you would disable the repository and re-enable the repository; when you re-enable the repository, Drone will start using your token.
If you want to do this in bulk you could use the CLI and write a bash script that lists all repositories, and then executes the repair command:
https://docs.drone.io/cli/repo/drone-repo-ls/
https://docs.drone.io/cli/repo/drone-repo-repair/
Update:
If you delete this user from Drone, it will re-assign all repositories owned by that user to a new owner, assuming a user exists with the same repository permissions.