Inbound email action - create ticket and update with Subject of email

Hi Team,

I have an requirement to create and update ticket with subject line instead of watermark. Client will send emails from JIRA system. They will have unique subject for each ticket sending to SNOW.

for example:

Subject: JIRA TKT NO 74 

So I need now to create ticket for the first email and next emails with same subject should be updated. Client did not have feasibility to send thread of emails , and everytime they send as new emails.

Please suggest code to do in inbound email actions

Help much appreciated. Thank you!