Ppm and pH how to adjust levels

I’ve been having some yellowish in my plants and I’ve been posting pictures and everybody told me I need to check my pH so I checked PH is all the way down to like 4.9 and my ppm on one plant was 765 all others are like 1689
What can I use to bring up the ph


I have the same question too.
How do you adjust ph levels?

Thank you,