How can I give a number to an absence that has been entered?

Hello,

We want to give a number to these absence records AFTER people enter a absence record. Thus, we will use this number as the form number in the notification that will be sent to HR after the absence is approved.

For example, person A entered a absence and submitted it for approval. AFTER SUBMISSION or APPROVAL gave this absence a number 433. How can I do this on HCM?