This video should help you. I’ve had great experiences with Nikwax, they also offer washing DWR as well.
It’s important to use laundry soap without enzymes. Then dry it gently and add some water repellent spray to not ruin the membrane. How to Wash Your Waterproof Jacket | Patagonia
You should look at North Face product care for the best results. Personally, I use Nikwax Tech Wash for all my outerwear.