In your script:

pidfile=/var/run/mypid.local  
[[ -f $pidfile ]] && kill -s 9 $(cat $pidfile)
echo "$$" >$pidfile
  

In your script:

# store the Process ID here
pidfile=/var/run/mypid.local
# If there's a stored PID, terminate with SIGKILL
[[ -f $pidfile ]] && kill -s 9 $(cat $pidfile)
# Save our PID for the next run to kill
echo "$$" >$pidfile
  

and, to clean up, just before you exit,

rm $pidfile