Stopping a program in an i-Motor is done by sending an END command. This does not stop motion though; that is done with the K command.
If a program is running and an END will not stop it is may be necessary to follow the below procedure.
Within the first 200 ms of power up, if the i-Motor receives a bunch of E's then it will not run the power up program. Type a bunch of E's (EEEEEEEEEEE) in the terminal, turn on the power and hit enter at the same time. This should stop the running of the power up program. Since this is time and reaction dependant it may take several attempts before the program will stop.