You could call Delta and if 1B better accommodates you with your service animal, Delta has to swap seats for you unless someone similar is already in 1B.

While traveling with a service animal, airlines are required to accommodate you anywhere in the same cabin. Main and Comfort+ are considered the same cabin, so technically you don't ever need to pay for Comfort+ to guarantee a bulkhead Comfort+ seat with your service animal. Some say this is cheating, but if you're only paying for C+ because of your animal, then that's not fair.