To use this action, you must first set up a Manual Flow that can be triggered from this flow.
Once the Manual Flow has been created, add the Trigger Flow on Related action.
Select the App where the manual flow has been created.
Note that the current App must have a Relationship Field to follow to the App where this manual flow has been created.
Follow the Relationship direction. Remember, if there are no fields to select in the Using Field, this direction is not followed correctly. Reverse the direction and try again.
Select Trigger a Flow in the above App in the Next Step and select the Manual Flow created.
See the Trigger a Manual Run page for a working example of how this is used.