Can someone explain the whole dominant and recessive part of the omegaverse? All I underst...

Dominant and recessive are scientific terms used to describe genetic traits.

Brief explanation of the science
Offspring get their genetics from their parents (half from each).
Genes are paired up one from each parent.
Two dominant genes get the dominant genetic trait.
Two recessive genes get the recessive genetic trait.
One dominant gene x one recessive gene get the dominant genetic trait.
(There are some dominant gene x recessive gene combos that can give unique traits).

In some cases with dominant gene x recessive gene the recessive trait can be activated by outside stimuli such as viral infection, side affect of medicine, etc..
An example is developing an alergy. In worst case scenario could be an autoimmune disease.
(Very basic explanation)

How the author seems to have applied this to the omegaverse
There are dominant and recessive Alphas and Omegas.
The dominant of both appear to have stronger pheromones.
The dominant Alphas seem to be able to control their pheromones to be able to influence Betas and Omegas. (And apears to be the expected behaviour of dominant Alphas)

The recessive ones seem to have delayed development of heat for omegas (and assuming rut for Alphas). A trigger induces the first heat/rut.

For Hyesung the trigger for his heat is either the Alpha pheromone perfume or Dojin (Alpha or fated mate). At this point the author hasn't revealed which and even if fated mates are a thing in this omegaverse so could just be Dojin's dominant alpha pheromones.

The doctors (at least try to) explain that a recessive omegas first heat has strong pheromones which eventually lessen as the heat stablizes.

I assume that pheromone strength is determined by which genes are inherited. I also assume that the first heat in recessive omegas is a species survival trait to attract a mate asap because of getting their heat at a much later age than normal so as to conceive asap.