Assigning a license for a user can be done on the Manage Licenses page for the Yoxel Sync package. Here you can select new users and remove licensed users.
Proceed to Setup > Click Installed Packages (see link on the left in the App Setup section below the Salesforce toolbar) > Click Manage Licenses underneath the Action Column > Select Add Users or Remove multiple users.
Click Add Users to include new users to Yoxel and select who you want to give licenses. Click either Add All Users or Add button. You will only be allowed to add users up to your Allowed Licenses total. You can purchase additional licenses by following steps in this article.
After adding a user, the user should be able to access the Yoxel Sync tab. If a user has any issues accessing the tab, check their profile settings to ensure they have the correct permissions: Enabling users to access Yoxel.
Once you've finished assigning the licenses visit the 'Configure' page of the Yoxel Sync package and go to 'User management' menu. You can activate the sync for the newly licensed users from this page. Click 'Add new users' link to do so.
Note: If you have installed Yoxel for Salesforce with access to admins only, users with other profiles will see a message saying that they are "Unable to access Yoxel data" when accessing Yoxel. To ensure that these users have Yoxel tab and application access see this artarticleicle.