It's not clear exactly what you want to do.
you want to add the script in /home/ddmsuser/DDMSPurge/ to your existing list of cron jobs.
If so, execute crontab -e
from a terminal, and add this line:
* * * * * * /home/ddmsuser/DDMSPurge/scriptname
Replace the "* * * * * *
" with how frequently you want the script to run (all *'s means to run the script once every minute--see man 5 crontab
Replace the "scriptname
" with the actual filename of your script.