If you want to buy prefabricated version of this Ozone has something called a "trimmer bracket" which you then buy the red ball separately.
https://www.ozonekites.net/proddetail.a ... er_bracket
Ozone provides some amount of support if you are retrofitting this, ask them and they should be able to give you a pdf that shows how you replace it on an ozone kite which should be enough to figure out how to convert your own kite.
I like making my own stuff.
Above is a nylon 1x1 inch block, but I have recently switched to using 1x1 aluminum (easier to work than nylon but a bit heavier). You drill a 2mm half way and then a 3mm the other half way through, that's how the lark's head is stopped inside the block. Then two 5mm holes for the attachment for the chicken line.
Of course you can always just buy a regular swivel nothing wrong with that. I don't like using a simple o-ring with a red stopper ball because the red stopper ball can get wear. Rather just have this nylon 1x1 block.
There are other systems people use, but I want a system where I get at least 10m of flag out so it works with my larger kites. The block will flag out until the control bar hits the kite just like a swivel.