Let's move a / one step forward and three steps back / backward and see ...

[Tan Elaine]

Let's move a / one step forward and three steps back / backward and see who can do so the fastest.

Which word in each case should I use? Thanks.

 

[Tan Elaine]

Could someone please help? Thanks.

 

[MikeNewYork]

Could someone please help? Thanks.

Because you are using "three" and "forward", I would use "one" and "backward".

Incidentally, although you seem to be describing some sort of activity, you have come close to an idiom, mostly used in business. To move "one step forward and three steps backward" means to appear to be making progress but actually losing ground.