Answer:
-Haz.
Step-by-step explanation:
The correct way to say it (in this case) would be:
-Haz lo justo. (tu)
You can also say:
-Vinimos para hacer lo justo.
Then, depending on the person (and also the context) you are talking to you could say:
-Usted haga lo justo.
-De manera tal que tu hagas lo justo.