と isn't being used with a volitional here. とするなら、とすると、とすれば are expressions to make conditionals. Here is an example from the answer to the related post I've linked below.
If my friend is going to come, it will probably be in May.
All of these expressions are constructed as "Aとする＋conditional expression", which essentially means "Assuming A, then B". とするなら is no exception here. とするなら＝とする＋なら, 「なら」 being the conditional expression here.
In your case, you have
If you're going to use it, (...) is the kind of sentence you would write.
If you changed it to the volitional 使おう, you would get a slightly different meaning:
If you're going to try to use it (...)
Related Post: What are the purposes of としたら, とすれば, とすると?
Further reading & more examples: Supplementary Suru (とすると etc. is at the very bottom of the article)