I don't think anyone's answered this question in here.
To drop one bomb you can:
A) Click and swap to missiles before the second bomb drops
B) Drop both bombs and resupply only one bomb. I forgot exactly how this works but it's something like if you fly over again and restock a second bomb you'll be in single bomb drop mode, or maybe if you don't drop it and restock a second bomb you're in single bomb drop mode... Try both out, I don't remember.
To drop one bomb you can:
A) Click and swap to missiles before the second bomb drops
B) Drop both bombs and resupply only one bomb. I forgot exactly how this works but it's something like if you fly over again and restock a second bomb you'll be in single bomb drop mode, or maybe if you don't drop it and restock a second bomb you're in single bomb drop mode... Try both out, I don't remember.