How different are they? Is one swollen? It's normal for there to be a slight difference in size, but not if one is swollen or there is pain.
If there is, you need to see your doctor very soon.
Normal just like a woman were one breast is slightly smaller than the other, Stay safe.
How old are you? Usually up until around age 25 you can get occasional testicular pain. As for size difference, that is normal, They usually even out.
if it's a slight difference there is no reason to be worried about it's normal but it causing pain or something else then you should visit a doctor.
Thanks have a nice day