So in your case I would :
Take away the things you can take away without making the tank a total mess, or take away as much as you can and leave it to settle again.
Clear an area up to the front glass so it is easy to get a net down there without getting it entangled in something.
Wait untill the fish you want to catch is happily swimming in the area, slowly get the net down behind it. It may of course dart like an arrow to the back of the tank, – and then you missed the opportunity, but if you don’t stir up everything and make the fish totally scared, it will come again. Or you can try when you feed.
Use a medium size net, not the small ones, – the small one is fine, but its easier to target it with a bigger net.
If you have to, in the end, clear most of the tank, – well, then so be it, but leave it to settle, maybe a day, – then you have a chance of seing which fish it is you have to catch. I must say, – for me, – sometimes it just takes a long time, more days, before I am sure I get the right fish, and I am able to catch it. In your case, I quess you could decide that it doesn’t matter if it takes a bit of time, better to do it without too much disturbance.
I have heard that some people think catching them in the net can cause damage to the skin, – but I have no idea how you would catch them without a net :S … even I would like to.