Following this answer, I was able to convert from GDA94 to GDA2020 using proj string (I'm using PostGIS).
Now is there a way to convert it back? I tried to invert the signs from @JasonD answer but it didn't work:
+proj=longlat +ellps=GRS80 +towgs84=0.06155,-0.01087,-0.04019,0.0394924,0.0327221,0.0328979
When I use the above string on the converted geometry the coordinates are not the same from what they were before the conversion.
Can someone advise how to do it?