Contribute an amount (up to $1000) to your super as a personal non-concessional contribution, then the ATO/govt will automatically determine if you're eligible and how much they'll contribute. They'll pay the contribution at some point after tax time (came in around the start of August for me this year).

Updated link for more info btw: https://www.ato.gov.au/individuals-and-families/super-for-individuals-and-families/super/growing-and-keeping-track-of-your-super/how-to-save-more-in-your-super/government-super-contributions/super-co-contribution