Translation:You swim there, run back, swim there, run back.
Why is the fourth "you" missing? Either four or just one "you" would be correct.
I guess that slipped in somewhere. Feel free to report it if it pains you. :)
You can include the "you" all four times if you really want to emphasize the repetition. Or you can just include the first one. Either way is fine.
Why not just: Swim there, run back, swim there, run back.? How would this be translated into Hungarian?
That would not indicate who is running and swimming. " You" needs to be included, otherwise it is an instruction for which the imperative form of the verb would be required and we haven't come to that yet.