How to mutate watch in GitHub's GraphQL API?

Question

I am using GitHub's GraphQL API for a project and I am expected to star or watch a repository. I am able to do the mutation on adding a star. Watching, however, has no word under the mutations. What am I missing here? I did quite a lot of research and came up with nothing. How can I do a mutation on the watch? Isn't there a keyword to watch a repo?

The mutation for adding a star is below. I am expecting something similar to this.

 mutation AddStar($repoid: ID!) {
          addStar(input: { starrableId: $repoid }) {
            starrable {
              viewerHasStarred
            }
          }
        }