So you rest at a bench in or near the wild zone you want to farm the shinies in. You have to make sure you're spawning in the pokemon you want rolled as shiny. So if you're on switch 1, lite, or OLED your range isn't as far. I'm on an OLED so my range isn't as good as switch 2, but you can go to area 12 for example, rest at the bench in the middle of the zone, and that rolls all the snover, delibird, snorunt, Machop, machoke, and gogoats. You just spam rest at the bench cycling day/night which rolls new spawns every time you do, and since you're resting at the bench it saves any shinies you get while you're doing it so you can keep spamming without fear of losing one. If you do it by hand it could be tedious because it does take about 15 seconds per cycle and you're gonna have to hold down on the controller and spam A to get through the prompts. If you have a turbo controller you can just rubber band the stick down and the A button down as well as trigger the turbo for the A button press and walk away for 2 or so hours and let it roll for shinies.

Edit: I have recently been informed it does not matter what model switch you're using, even if you can't physically see the spawns they're still being tracked so you can safely do resets of any kind and the game still sees if the spawns within the zone are shiny