From the Model Mayhem FAQ:

How do I edit Praise on an existing credit?
Editing praise to an existing credit is easy!

  1. Go to My Stuff
  2. Open My Credits
  3. Find the person whose Praise you want to edit. You should see something like this:

  4. Click "Edit Details" and from there you should be able to modify what you typed in for your praise.
The other person will then have to re-verify the credit to accept the modified praise.