A lot of people try to compensate for this by doing exercises that use both at once, they think that by using both arms they're working each arm in equal proportions. That is not the case, when you do an exercise that requires two limbs and one is stronger than the other, the dominant limb will take over, meaning that it takes the strain away from the weaker limb and leaving it behind. So you should actively isolate the weaker limb, this doesn't mean that you should completely ignore the dominant limb as you would be wasting the progress you've already made. For example, if your left arm is weaker than the right arm, you should do maybe one set of bar curls and then a set of left arm only bicep curls, this way you're working both arms but putting the emphasis on the left arm in order to make it as strong as the right arm.
If you have a limb that is weaker than the other then I strongly advise getting that limb up to scratch, not only will it make your body more symmetrical, but you will be able to go heavier/ longer in exercises that do require both limbs.
As always, good luck