The bird sounds territorial. Is he aggressive when outside the cage? I would start with hands-off training to get him used to you.
Most people don't realise stepping up is not a command, it's a trick. If the bird doesn't have an reason to step up, it won't. Birds need a different training approach to dogs for example. While dogs aim to please their owners, parrots don't. They are self-serving creatures and will only want to interact if they have a reason to.
It sounds like the bird takes treats. The very first thing I would do is target/touch training. Simply put, target/touch training is getting a bird to touch the end of a stick. Here are some videos that explain it in more detail.
Target training is helpful because it is a request from you to the bird in a language that the bird understands.
When I first got my rescue galah, he would bite constantly and wouldn't step up. I started target training first which really helped when I needed him to go somewhere and I couldn't grab him.
There are many more things I could go through, but this should hopefully be a good start.