How to add button to PM screen

[SVTCobraLTD]

I want to move a button I have on the left side of the PM to the right with the rest of the them. Basically the "Report PM" button needs to be moved right next to the "Forward" button. See attached screen shots. Screenshot 1 is current, screenshot 2 is how I want it. I mainly just need to know the file to make the edit in, the rest I can figure out how to do. Thanks in advance.

[Triky]

It should be the postbit(_legacy) template..

[SVTCobraLTD]

It should be the postbit(_legacy) template..

For the private messenger system? I thought that was only for posts.

[Dismounted]

Postbit templates are used much more places than just for posts.