Frontloader pair that's currently stacked and is to be separated side-by-side? Toploader washer with frontloader-match dryer? Why is there an issue with leveling them? A photo would perhaps be helpful to clarify what's the concern.

Is the problem mismatched heights -- that one is taller than the other?

Add wood under the feet, if the current feet aren’t adjustable enough.

Sounds like the washer and dryer are not the same height?

You could build a sturdy platform to bring the shorter one to the same height. However if the washer is shorter, be aware that vibration could have it vibrating right off a platform. A built platform can also be tricky when the washer has to be pulled away from the wall for repairs, etc.

My washer and dryer are two different brands and the height difference is approx. 4" . It does not bother me. Our guests don't see it and photos of my laundry room will never be in a magazine. ;-)