How to modify body of 'Hold Incomplete invoice' mail notification

Hello,

Users (Assignees) are getting mail notification when any invoice goes on hold and want to modify the body of the email as it doesn't have much relevant details to understand the purpose, the vendor, issue and what action is needed, etc and also kindly let us know what the source of this mail notification is.

Kindly provide the insights it will be helpful for us.

Attaching a sample mail screenshot which users are getting.