You won't quickly eliminate all of them, at least without killing your superworms. If you just try to wash the tub and start again doing the same thing, you'll miss a few and quickly be back to square one very quickly. They aren't exactly harmful, but they're annoying and they'll multiply quickly and eat all your oat bran etc. The way to deal with them is to change the conditions so that they're not favourable to the mites, the mites will very quickly reduce in number so that you'll barely notice them, and after a while they'll disappear completely unless you have a reserve colony or source of continual reintroduction, but as long as you're keeping the conditions correct, you won't have any problem with these mites. I call them citrus mites because of the smell they make when you squash them.
Fortunately, the ideal conditions for your superworms are hostile for these mites, so by making things bad for the mites you'll make conditions better for your superworms. I see you're using a Quadrant tub, it looks like you don't have any ventilation in the lid. These mites thrive in high humidity and low air flow. Superworms can't climb Quadrant tubs, so either leave the lid off, which in itself should solve the problem (lower humidity and more air flow) or use generous ventilation. If you still have trouble, put the superworm tub on a warm surface (I use the top of a snake cage) which will dry it out and keep the insects nice and warm which will make them grow faster too, and make sure you always leave a water source (I offer small pieces of carrot once or twice per week). Even if you have a huge infestation, it will vanish almost literally overnight with the right conditions. The dry conditions will help prevent minor fungus/mould issues which will improve the health of your colony and you'll get better hatch rates with your eggs.