There is a slight difference in strength but its not huge. Sometimes I'll struggle a bit more on the last 2 reps with my left then my right.
For starters use dumbells a while and do sets for the weaker side first. However many reps you get, do 1-2 less for the strong side.
Honestly I had the same issue and I found a simple exercise I had never bothered to do that has solved it completely. Bilateral dumbell preacher curls. No clue why but for some reason it seems to really force each side to do it's own work. Has done wonders for my biceps, and I mean wonders. For triceps I have a slightly smaller left side so I start with one arm cable pressdowns cross body ala Dorian and make sure to get 1-2 reps more with my left side and focus on the contraction. You may find like I did that the stronger/bigger side seems to contract better than the other. I think it's a strong mind muscle connection thus slightly higher reps will, over time, build the connection to the weaker side until it matches the other.