There are several ways of resetting the light. The easiest is to disconnect the battery. This will erase everything. Clock, radio presets, window auto open and close points, etc. Another option is to pull the EFI fuse. That will erase the codes causing the light.
Now for me, I would be concerned about why the light is on. Replacing the alternator shouldn't cause that. I would go to a local parts store and have them scan the code to see what it is. The scan tool can also delete the code and reset the light.
Your auto down and up need to be relearned because they obviously disconnected the battery to replace the alternator. At least they should have. You might find the source of the problem if they didn’t.