Question

Do this or you will be punished (convert into complex sentence)

Answer 1

You will be punished if you don't do this.

Answer 2

The answer is: Unless you do this, you will be punished.  Here the sentence is transformed into a complex sentence where the principal clause is “you will be punished”.

The secondary clause is “unless you do this”.

The original sentence was a compound sentence added with the connector or. By adding unless, the meaning has got clarified and it reads well.