...

I think it's maybe the Alpha scent that his brother's company makes, but not sure. http://www.mangago.zone/read-manga/love_is_an_illusion/uu/tr_chapter-5.1/pg-9/

But what does he want with it? Is he manipulating Dojin?

I don't know, he's a Beta and faced discrimination because of this (even from Dojin's brother who dismisses him as a beta), so maybe he bought the Alpha perfume for personal use. I don't think Dojin cares whether his friend is a Beta, that's why Heeson is so devoted to him in the first place. This is just speculation, others might be able to clarify though.

Probably omega pheromones

That's kinda what I thought, that they are manufacturing Alpha and Omega pheromones and targeting the Beta 'consumer' and for those who have weak pheromones of their own..

But so far in the plot the brother's company has been shown to only produce Alpha perfume. What benefit would a beta have in taking omega perfume, when this will open them up to further discrimination . In this interpretation of omegaverse it seems like Alpha's are the only ones with status, whereas Omegas are pitied and exploited . I think it's more reasonable that in such an environment Heeson tries to disguise his identity (which he too is insecure about) as it means in his working environment he gets to blend in or be given a bit of status, or at least by using the perfume it gives him confidence to feel like he could be an Alpha, just as how Hyeseong deluded himself in order to get through the day rather than accept his identity.

Clearly his family make the stuff! XD
BUT WHY the bottle?
--What does he intend to do with it?--

He probs wants a piece of "Master"

lol, my answer was just a guess. I always considered Betas as neutral with the most normal life. But who knows, I'm sure some Betas wish to be Alphas, or possibly use the pheromone perfume for sexual roll-play (Alpha or Omega anyone)? Also I know the Omegavers is different depending on the author. But your answer is good explanation :) The only thing is that Hyeseong didn't find out till chapter 4 that he was an Omega and when he used the pheromones perfume in chapter one he was still under the impression he was just a weak Alpha (having come from a family of Alphas), he was at that time just trying to boost his Alphaness. XD