Appointments > Appointments > Specific appointment you want to modify
Click on the appointment
Under "Master", use the drop down menu to reassign the appointment to another trainer.
Save
The appointment will be moved to the specified trainer's appointment calendar.

*Note: reassigning the appointment moves the appointment to the specified trainer's calendar, but it does not modify payroll. If using appointments to generate payroll, the modification to payroll for each coach must be done manually.