Track transactions from a starting balance and date?

Hi, I’m from Australia and have spoken to the Australian Tax Office about my crypto holdings. I explained that when I first got into crypto, it was only for purchasing goods and services but I have since moved more into the investment side of things from March 2018.

The Tax Officer stated that I could start my records from the date I moved to an investment usage (March 2018) with an “opening balance” of any holdings with subsequent transactions recorded for capital gains purposes only.

Is there any way I would be able to set this up please?