Overview
This article covers the steps to edit a template you have created that is set to be emailed at a future date.
How To Edit
To edit a scheduled email, head to Settings > Communications and select Templates from the top of the page. Find a scheduled template, which is one with a timestamp on it. For example:

Select one of these templates, and in the upper right hand corner of that screen, you can click on the ellipses in the top right and choose "Edit".

Then you can edit the schedule and then the template and save it for future use!