Here is something that might help steady your dog. Have him on lead at heel you holding the lead, taut at first but no pressure. Have bumper/toy/bird whatever he will break for. Stay him, throw object with Hey Hey Hey if that is more likely to get him to break. If he pulls against the lead to break, you go and get the object. Repeat until he does not pull against the lead then let him retrieve the next one as his reward.

Repeat with a loose lead. Gradually do up to 4-6 throws before he gets to retrieve one as his reward for being steady. This is good for all unsteady dogs, their retrieve is their reward for being steady.

You can then have a thrower and repeat the same thing. Start with thrower close and then move thrower farther away. If he breaks make sure the thrower gets the object before he does, so keep the throws close to the thrower for this exercise.