There are two possible situations:
1. Tony's thinking is transformed into some small-scale movements, such as small-scale movements of arms, fingers, legs and other positions within the allowable range. After the auxiliary system captures this action, amplify the amplitude into the action of the outer armor? For example, if you extend your left index finger, it means a left fist.
Disadvantages: It doesn't sound cool, and it takes a long time to establish the mapping relationship between small actions and big actions.
2. Tony's thinking is directly transmitted to the armor through the electrical signals of nerves, and at the same time, it blocks the transmission of nerve signals to the body, making the armor move without making people move.
Disadvantages: According to the comic book Iron Man Volume IV and Invincible Iron Man, this technology can be realized on Tony after desperate transformation, but the movie version has no relevant plot foreshadowing.
Personally, I think it should be through neural control, because in the third movie, Tony once had a real person in the cabin, wearing a helmet, using neural control to manipulate an empty shell mecha to save people on the plane, so it proves that in the movie world, Tony has completed such technical transformation. In addition, in the third part, there is a passage in which Pepper goes home and does some actions to Pepper, but at the same time it does not affect him to control his body to do sports.
So this problem is actually a small loophole. Of course, if anyone has the English HD version of the picture I posted before, you can see what the production team has to say about the armor setting.