Are you able to do this work? If you think you can, then go for it. My advice is to buy a replacement freehub body to have on hand in case you need to replace it one day or yours doesn’t get all the way back after you flush and lube.
If you can’t do the work, take the bike in to a bike shop and have a new one installed. He the older one back and then see if you can get them t to work again.
John