I’m currently away from my keyboard but I think you should be able to accomplish this by adding a AddRow() action after the “send email” one you already have (both actions will need to be wrapped within a RunActions()) and for the value to input in the field meant to store the user, you could use User() …
Your formula would look similar to this :
RunActions (
[Action 1: Send email],
Table.AddRow(
[Field meant to store the user],
User()
)
)
Sorry I can’t do more at the moment but I hope this helps a little