Adding or modifying an entry on AniList is an easy task. The main focus is making sure that data is accurate and as complete as possible for that moment in time. All sections of the form are formatted in a similar fashion and have handy tool-tips to assist you.
Existing anime and manga entries can be edited using the edit button at the bottom left of their page.
Existing staff and character entries can be edited using the edit icon button at the top right of their page.
When a user provides a submission it will undergo a review process where a moderator can approve or deny the additions and/or changes made - it is extremely helpful to provide as many sources as possible to confirm the information you want to submit.
After making a submission, you will be able to view the status of your submissions, plus receive comments and questions from any moderators working on it if required.
Submission panel on a users' profile page.