The first step is to take your beef shank and soak it for 1 hour in cold water to draw out the blood. Then put it into your Instant Pot and cover with 4 - 5 cups of water. You just need enough water to mostly cover your beef shank.
I have an 8 quart Instant Pot and could fit the whole shank in without cutting it. If your Instant Pot is smaller, you can cut up your beef shank into 2 or 4 pieces to fit into your pot. Just make sure the liquid covers the beef.
Next, cook your beef shank in the Instant Pot under high pressure for 30 minutes. Once the 30 minutes is up, release the pressure and transfer your beef shank to a pot.
Add about half of the liquid from the Instant Pot to the pot with the beef shank. Again, you just need enough liquid to cover the beef. Add the dark and light soy sauce, 5 spice powder, white pepper, star anise, and salt to the pot. Bring to a boil and simmer for about 10 minutes. Then put the lid onto the pot and turn off the flame.
After the beef and steeping liquid has cooled store in the refrigerator for 24 hours, turning the beef once or twice to ensure all parts have a chance to soak in the braising liquid.