Sand filter steps/settings to lower water below tiles

Please, can I get step by step instruction and all settings to lower water level 4" below tile line?

I think the pump sucked air alternating with water-to-waste last year.  Pool supply company said that was ok, gurgling was normal.  I’m not sure that is true.  I have been unable to find online the info needed,

Thanks for any help.  Carol W.

Forgot to say it is a sand filter.  I was fine with d.e. filter for 38 yrs, until 2019.