For managing a sub category you can either edit or archive.

Path: Space > Ellipse Icon > Settings > Categories

Select your desired space to see the Ellipse Icon.

Edit Sub Category

To manage the sub category click the Ellipse Icon on the right of the sub category box and click on the Edit option to edit.

Now you can edit the sub category details then click the Submit button.

Archive Sub Category

Next to archive a sub category click the archive option.

You can view the archive sub category by clicking the Filter button.

Path: Filter > Archive

Restore & Delete Sub Category

For the archive sub category you can either restore or delete them. To restore click on the Restore option.

Next to delete just click on the Delete option.