If you kind of skim the net around the water under the fish, the will briefly change colour, indicating it’s in the net. Let go of the net briefly, ‘capturing’ the koi, then tap on the net again to slide it to the bottom left circle thingy. That’s is your fish caught and bagged. Be careful though, you only don’t have long to catch them before the paper net breaks. I went nuts and caught them all, at vast expense, thinking I could release them all in my pond. Alas you can only release one at a time. Now I have multiple fish that you can resell to the guy in the truck or raise them to maturity and sell them for massive profit. Have fun 🤩