Making 1% milk into whole milk
You can't directly make whole milk out of lowfat milk and milkfat. But if you like, you can try adding back some fat to the recipe -- melted butter or vegetable oil -- at the concentration of, I suppose, 2.5%. (If the recipe already includes one of these, just increase the amount.) The result will not be quite the same, but will be very close.

In a yeasted bread, though, the difference between 1% and whole milk probably won't be significant. I'd just use the 1% milk, and see what happens.