Subject:
 
[Insert Date]: Session Ammendment
 
Body:
 
Hi [Insert Bookers Name],
 
I just wanted to reach out to discuss the possibility of making a small change to [Client's Name]'s upcoming session as a one-off.
 
Timing Change:
Would it still be convenient for you to attend the upcoming session at [proposed time slot]?
 
Coach Change:
The upcoming session will now be delivered by [coach's name], instead of your usual coach, [coach's name].
 
The reason for the change is [Insert the reason for the change].

Please let me know your thoughts on the above change when you get a chance. As I mentioned, this would be a one-off for this week. 
 
Thanks in advance for your understanding. 

Best regards,
 
[Your Name]