It's possible to copy a Recommend rule from one model, index, or replica to another, as long as both indices are included in the same application.
- Go to your Rules page belonging to the Recommend feature of the original index
- Click on the three dots to the right of the rule you'd like to copy
- Click Copy Rule to Model
- Select which models, indices, and/or replicas to copy the rule to
- Click "Copy Rule to Model"