Currently, there is no way to recall the Letter of Recommendation request. 

Instead, you have two options. Both options start with impersonating the family, viewing their Checklist, and clicking on the blue title for the recommendation step in question.

Your two options are:
  1. Choose to resend using the same teacher's name, but your school's admission email instead.
  2. Choose to resend to a totally different person (for instance, the school and the school's admission email).
Both instances allow you to complete the online submission on behalf of the teacher. The submitted file shows in the File Submissions area.

Alternatively, you can go to the Candidate's record tab, add a new recommendation, and manually use the Checklist option there to mark it as completed. This will still show as "Requested" to the family, but it will have the green checkmark indicating it is completed.