Re waterproofing a down jacket

[Happyinheels]

Looking for tips on how to wash and re waterproof a down coat please. I have a North Face Arctic Parka which has lost its waterproofness! Is it something I can do myself? I love this coat and want to get it ready for winter. Thank you!

Nikwax products

Thank you @saltnsaucey Is this something you've done yourself?

I'd contact TNF direct and ask them. I sent some walking boots to them once and they redid the whole tongue and lace system (the boots were about 2 years old).