Hi @Deepika61 ,

you can implement this functionality with Flow designer or Business Rule. I have configured it in Flow designer.
In Flow Designer...
1. Trigger

2. Action

•  In if condition select you backend field from the HR case form and
• In Then create action "Ask for Approval"

 If you need I can help you with business rule as well..

Mark my answer correct and give 👍if this helps you...

Thanks,