How do I re-assign the same skill, but get access to different questions?

We are working on Decimal place value names (tenths, hundredths, thousandths, etc). About 50% of my students failed the first assignment so obviously, I have to reteach. We always do "the same questions" and take them up. On the assignment > assign page, I see that there are 21 different questions ("show all possible 21 questions") that students may come across in their "do these 7 problems" assignments. How do I re-assign the same skill (decimal place value names) but get access to different questions?