I want to design a setting not to let user to close the ticket unless specific fields are filled

I think what you're trying to reach is to be activated in your workflow.

1. Open the workflow edittor for the required worktype

2. Select the transition you'd like to restrict

3. IN the bar on the right scroll to "Rules" and select "Validate details"

4. Choose validate a field

5. Choose what to restrict & confirm

6. Update workflow - refresh the item and try again

I think this page explains it in more detail if required.

Hello @Kotagiri_ Haritha 

In your workflow and your transition you need to add the Validator, choose the field and also what the error message will be.