In the same way that regular humic acid and nutrients would be.
2% humic acid is 20 grams/L so I would calculate what it would cost to make myself and add a dash of trace elements for a couple cents from a bottle of store bought trace element fertilizer.
Eyeballing math: Humic acid is about 17 dollars a pound, 430 grams or so. A bottle of trace elements is 7 over here. So for about 30 dollars combined you can make 21 liters.
This stuff is 8.99 for 230mL, so around 31 dollars/liter.
A DIY solution would save you roughly 21x the costs, and it's just a mix of three things: water, trace element fertilizer and humic acid.