Open a article, read the key phrase in the top. Example: Keywords: kitchen decor
here kitchen decor is the key phrase.
Change the H1 and H2 copy to include the key phrase or add it in some where else, like make a header more.
Save and close. This is very quick, often less then a minute if you are good at English. Max a few minutes. But not the first times, one need routine to get into speed.
Please do this as soon as possible as this is PLR articles and gest old very fast.