Im only new to saltwater also myself.2 months ago filled tank with water and cycled.
Just lots research 5 years ago ehen nearly set tank up then research these last 6 months.but as we all know research/ reading different than hands on experience.
But to lower your salinity you would have to take some saltwater out and add fresh rodi water ( i prezume your using rodi water) to lower salinity.and remember all the heat in tank and that surface agitation causes evaporation so when top up the water,use fresh water also.as the water evaporates but the salt stays in the tank.
Your saying your salinity 1.020-1.023?
Why is it fluctuating?
Are you topping up evaporated water often enough by hand or better still using an auto top off device.as keeping the salinity stable is important.
Alot whilst the tank is cycling use this time to get familar and perfect the use of all devices in tank.
Like flow from power heads ( dont want sand bed blowing all over)
Return pump speed if adjustable and make sure your sump if got one can handle all the extra water from a power outage turning the pump off and draining back into sump.also that return nozzle in dt not positioned to deep in dt water as causes more water to drain back into sump unless hole/ siphon break drilled.
Playing/ tuning in your skimmer/ making sure not overflowing,can add a few wipes of vegetable oil at top of skimmer cup so as the bubbles hit it ,it pops the bubbles and drop into cup ( dont put vegetable oil in neck of cup and where rising water will be ( watch you tube videos on this)
Making sure the temperature of tank is staying stable and where you want it to be and extra heat from lights/ motors in pumps/ power heads isnt a problem ( if it is you can add a chiller or put a small fan on top of the tank or sump to blow accross it,but this causes extra evaporation so need extra top off water.
Mqke sure auto top off working correctly and set at correct height.
And basically fix/ correct any issues you may find.
If you dont want to take out the salt water and add fresh rodi water to dilute the salinity then you can just leave it as it is ,it will cycle if add battle bacteria/ use live rock or even if use dry rock/ dry sand and nothing live and do nothing or add nothing then nature will cycle it naturally as bacteria in the air will get in.some cycle in days,some cycle in a month or 2.and some even suggest a cycle of 4 months.so we just got to decide what we want to do.
I would strongly recommend some of the cycling threads on reef 2 reef as i been reading them and very interesting and educational,especially threads with brandon as ge been researching tank cycling and free amnonia and alot stuff in this topic.
Good luck and have fun and hope your tank gives you great joy