Change notifications after meeting is booked

Hi, 

I've booked many meetings but then I wanted to change something in the reminder email the clients will receive. I changed it in the services, but I can see in the Calendar, that the email remains the same as before.

I tried changing it directly in the appointment, but it somehow canceled the meeting. It's also a lot of meetings to modify! I don't want to have to change it for each one and everyone involved getting an email when I do. 

Is there a way to do it? 

Thank you!