Welcome to Dogsey!
If you haven't yet heard of BAT (Behaviour Adjustment Training) it might be worth looking into. Check out my thread on this - I've just begun using it for my dog-reactive PON, with good results so far.
If you have a basic understanding of clicker training then you'll probably be OK to try BAT by yourself when you're out and about. There's a book by Grisha Stewart (available through Amazon) and several websites with videos to give you tips.
I am still new to this, so please do take advice from qualified trainers/behaviourists too! However, The basic premise is that dogs have a threshold, a physical distance between them and the thing that freaks them out. Outside this is the 'safe' zone, where the dog doesn't feel threatened, then the threshold itself (where the dog signals he's starting to feel unhappy, by halting and staring straight at the object). Beyond the threshold means the dog is definitely not happy and it will start to react - barking, lunging, cringing, crying, shaking, etc).
You need to teach your dog you understand what he's telling you with his body language when he reaches the threshold, and YOU will take charge at that point. So . .
1. You walk your dog on a loose leash, letting him go wherever he wants, until he sees a 'trigger' (anything that makes him react in a way you don't want). He's at his threshold; he comes to a dead stop, looks straight at the trigger, maybe pricks his ears. This is his cue to you - he's saying "I'm not happy!"
2. The moment he looks at the trigger, click (or use a marker word like "Yes!") and/or call him to you as you walk in the opposite direction. If you need, verrrrrry GENTLY increase pressure on the leash so that he must come away. Don't yank it!! When he's with you, give a treat.
3. Repeat.
4. After a few trials of doing this, wait a second or two to see if he moves his head away after seeing the trigger, or licks his lips, or yawns, lays down - anything other than the behaviour you don't want! If he does, click, call him away, treat as he comes alongside. If not, just go back to clicking him just for noticing the trigger.
Once your dog feels confident he doesn't HAVE to encounter the 'scary thing' nose-to-nose, (ie, he can just turn away from it) then he should start to feel brave enough to gradually get closer and closer to it before he gives you the 'halt, stare at the trigger' cue.
Try not to let your dog go beyond his threshold. If he does, and starts reacting, then just move back into his safe zone again, and let him calm right down. Don't make him face the trigger again until he's had at least 5-10 minutes to de-stress, otherwise he'll react even faster next time.
If you can't move away from the trigger, use distraction; feed him treat after treat, so that his focus is entirely on you. He won't learn much but it might stop an unwanted reaction happening. If you keep repeating a phrase as you feed each treat when you do this, you can condition him to associate that phrase with a colossal amount of treats, and that can be used as a rock-solid recall later (ie, for when just calling his name isn't enough!). Grisha Stewart uses 'Treat Party!' which is fun, but you could say anything you like, provided it's not something the dog would usually hear/associate with anything else; NOT his name!
Anyway, I hope that gives some ideas to make a start, and at least feel there is SOMETHING you can do. Often, feeling helpless is the worst of it, isn't it?
Best of luck and let us know how you get on.