There are several steps required and several different ideas.
First, you need to calculate how much ammonia is added to the solution when you add 1 g of ammonium chloride. This is relatively easy to calculate using molar masses of ammonia and ammonium chloride.
Second, you need to calculate dilutions. These calculations are basically based on the mass conservation - whatever is put into the solutions, stays there. So, if you need a 38 L of a solution that contains 2 mg/L of ammonia, you need 38 L×2 mg/L = 76 mg of ammonia, and you want it to be present in 1 mL of the solution.