In Salesforce go to Setup > Apps > Connected Apps > Connected Apps OAuth Usage and scroll down to find Yoxel Sync app. Click Install if you see the button ot click Manage App Policies if the app is already installed.
Click the Edit Policies button to change Permitted Users to "Admin approved users are pre-authorized". Do not change anything else!
On the app policies page scroll down to Profiles and click the Manage Profiles button. Specify all user profiles that should be approved for Yoxel Sync.
Now navigate to the Yoxel Sync tab and go to a template that you want to activate to use this pre-authorizations mode:
On the first page of the template wizard expand Salesforce service and switch Authorization mode to "Use admin approved pre-authorizations". Then click Save.
After this you can step through the wizard and publish your template. All syncs under this template will start using this new mode of authorization and your users won't have to provide self-authorizations anymore.