the easiest option would be to integrate the approval into your existing Incident Process. First look for the place you want to insert the approval and insert a new Status e.g. "Waiting for Approval". Now you can move your Incident either automatically to that status or use a manual action e.g. "Submit for Approval" to get to the new status. Don't forget to put an automatic Assignment action in front of the status if you like to assign the Incident to the approver or the approval group.
Then you can add two paths to your new status. The first one with e.g. "Approved" Action and if you like with an automatic notification for the raise user. Then it moves on to the next status in your process.
The second path is for example the "Recect" path and contains an automatic notification too and moves on to an end status.
Just take a look in the out of the box request processes e.g. the Automated Software Request Process. There is everything in it.
You can fill in virtually any automatic action you like between the actions and the next status, so you can automatically inform the raise user, the user you ask for approval, etc.
I hope I could put you on the right track.