Login to Backend
Navigate to Design ➤ List Builder, you will land on the “List” page. Now open the list in Edit mode and you can see the Code Editor option at the bottom.
By clicking on the Code Editor, an editor will pop up where you can edit/paste your JS code. Once you edit/paste the JS code, click on the Save button and Publish the List builder record.
You can Preview the List builder to check how it looks.