ZenHub uses GitHub repo's native label set to populate which available labels exist when navigating Issues in ZenHub.
Creating labels in GitHub (to show up in ZenHub)
To create new labels, you have to work within GitHub. At the moment, labels cannot be created in the ZenHub web app.
In GitHub, navigate to the repository where you want to create or edit a label. Next, navigate to Issues and further click on Labels next to the search.
To create a new label, click New label on the top right.
You can also edit or delete existing labels in the same interface using the label table.
Creating the same set of labels across all connected repos
Since labels are native to GitHub, label-sets are repo-dependent. Because ZenHub adds a layer of being able to create Workspaces using multiple repos, we share a workaround to create the same set of labels cross-repo in this article.
You can also add your vote and comments on the feature request to make this more streamlined in our feature request product portal.
Why you might not be seeing an available label to assign an issue in a Workspace
If you've created a multi-repo Board, because labels belong to a repo, not a ZenHub Workspace, you might be misidentifying an Issue existing in one repo with the label you're looking for in the other repo connected.
Issues still belong to repos, so when assigning labels to Issues, only the available labels from the repo the Issue lives in will be available. At this time ZenHub does not pull in labels from other connected repos in the Issue itself.
Use the suggested creation of labels cross-repo workflow, using multi-action, to assign labels to Issues that might only exist in some of your connected repos.