Hey! Best of luck to you here as this is definitely going to be a journey. I have a rescue husky that also deals with this issue.
One of the main things we have been working on is being able to just acknowledge that other dogs exist. This is helpful if you have a friend with a dog to work on this task.
You need to find his trigger point, basically how close can he get to the other dog before he starts getting excited? Once you have a baseline of how far away you need to start you can really start working on this. My dog and I play a distraction game (i.e. "find it" - throwing small treats in the grass) before he gets over threshold. Mind you this is still like 20 yards away from another dog, but you just have to do this and slowly work on getting closer.