Simply add the DE into the skimmer, pump running, and allow it to be taken into the filter and deposited on the sand bed. The recommendation is to stop adding the DE when your filter psi increases by one lb.
Will it help you? Perhaps....there are those here that swear by it and there are those, like me, that could see no difference. It certainly is neither harmful nor permanent so nothinhg ventured, nothing gained.
Just wondering Dave . . . with the DE added on top of a sand bed, do you stand to lose a lot of it during backwashes?
The DE I'm familiar with is for household pests and is as fine as flour. Is DE for the pool filter much bigger granulate?