Hi,
Just would like to know where can I change the message after the online form has been submitted?

Would like to change the default message saying
"Registration Complete!
Your registration requires approval. Once approved you will be sent an approval notice to the e-mail address you entered.

When you receive the approval you will be able to log in."

Please advise which script code allows me to amend the default message.

A quick search turned up this thread as a short answer.
And this thread for a little more detail.