Edit a comment in signoff report of a closed task in workflow process

オフライン

The ask is to edit or change the comment in a signoff report of a closed workflow process.

the task is already in closed state with some comments as shown below

But now they wanted to rewrite the comment differently as per some requirement.

I couldn't find any direct ways in PLM to modify the signoff comment. Thought to do this from Backend. But i couldn't identify the relevant data table where the workflow process sign off history is stored. 

First of all Is this a valid request? if so how to modify the comment in signoff history? 

Please throw some light!

Thanks.