Have you completely emptied out? Fixing the bottom, I think, you are going to have to go from the inside. I would contact a good mason.

There's no easy way to fix that. You've got settling: part of that is supported by the concrete at the bottom of the steps and part of it seems to be sitting on dirt. I don't know how you would easily get a proper footing under the whole thing without taking it out, laying a pad, and then re-building it. Sorry, but I think this will be quite a bit of work to fix it properly.