What does "in reference to" mean?

It means that you are talking about something you talked about earlier.
Suppose you discussed meeting a friend and decided to meet at 2pm. You then chatted about other things. Then you might say "In reference to our meeting at 2pm. Can we change that to 3pm."

It basically means 'going back to', and it's mostly used in essays.
So, 'in reference to my earlier point' means 'going back to my earlier point'.
It's just a posh way of saying it, I guess.

In... Reference... To...

Hope this helps! This is the most simple way to describe it!