Belenios supports a dedicated voter interface for Majority Judgment, where voters give a grade to each candidate, such as "Excellent", "Good", "Bad", or "Reject". You can find here more information on the contexts in which this method is well suited and how votes are counted.
Preparation of the election
On the page "Edit Questions", you need to tick the box in the insert that starts with "Alternative voting methods (warning, still experimental)" to activate this alternative mode. Click on "Prefill with Majority Judgment" to prefill the field "Counting method specification". Edit this field to add more grades or modify them. A large number of grades is supported but you should test how it is displayed to voters ("Preview booth" on the main page of the preparation of the election).
The rest should be self explanatory. ;-)