Map the Email Subject to a header column in your spreadsheet (1).
Add the common data in the cells below and use the formula below (2) to pull in custom data from another cell in your spreadsheet. Copy and paste your formula to all cells where you wish generate a Mail Merge.
In the case below the formula we will use is
="Training program for "&A2
NB: Only copy formulas to cells where you wish to generate a doc and/or mail merge as the add-on will run on every cell where data is detected.