One of the best apps that I have found that can do that is BetterTouchTool. It is free for MacOS 10.6+ It allows you to create links from all kinds of gestures, and button combinations. It works for the Magic Mouse, Normal Mice, Touchpads, Apple Remote, Siri Remote, Etc.
I was unable to get the cmd+scroll alone to work, but cmd+shift+scroll works great. To get it working: Install from https://www.boastr.net/ then open the app preferences and go to "Normal Mice" for gestures. "Add New Button" then Hold down the shift key as you scroll over the action area. (3) Make sure to check the Shift and the Cmd boxes.
Add a "Custom Shortcut" of + or -
You will have to create an entry for scrolling up and scrolling down separately.
Limiting The shortcut:
In the left panel "Select Application" you can have the Shortcut usable Globally or only apply if a specific app is active, ie. only work if you are in Chrome.
Advanced -- if you only want the shortcut to apply to a specific app you can setup a "Predefined Action" -> "Send Shortcut to Specific App" You can then Choose an app that receives the + or -