A new fish may not eat for a week. It all depends on how long it takes to get comfortable. As the blenny is an omnivore it may be eating when you aren't around.
Did you see it eat at the lfs
Have you noticed it getting thinner and losing weight?
Dried seaweed with garlic extract? Is this sold for the aquarium?
You want to feed the coral beauty and blenny NORI which is also sold as sushi wrap. Get it plain, (probably toasted) as any Asian market or the local grocer. Use a clip or roll it really tight and rubber band it to piece of rock rubble.
It might take a few days till they go for the nori too. Whatever is not consumed in 24 hours should be removed and replaced.