To add a shortcut key combination or toolbar button later if you didn't assign one when you created your macro, don't go to the Macros button.
Instead, go the Microsoft Office Button at the upper left of your open document, click Word Options, and then click Customize. In the Choose commands from dropdown list, select Macros and you'll see a list of any macros you have available. If you want to add a macro to your Quick Access Toolbar across the top of your document, simply select it from the list, click Add >> and then click OK.
To add a keyboard shortcut, click the Customize button at the bottom, select Macros in the Categories section, and then click on your macro on the right side of the box:
Enter your shortcut key combination, and then click Assign in the dialog box and OK to close Word Options and save your changes.