Unilateral training, including the weaker parts of the range of motion. Partial reps just through the weakest or most difficult part of the ROM will also help. This can be done after the full ROM exercise is completed.
I’ve found that one extra set on the weaker side is a good gradual way to get it to catch up. More than that can sometimes lead to other imbalances. Also using the weaker or non-dominant side for daily activities can help too.