Source: barre + bag
Then, stitch one long ribbon in a U-shaped pattern (secure under the drawstring casing on one side, continue under the arch and up the other side). That helps pull the shoe towards your arch so that it’s more flattering.”
Source: Mary Carpenter for Pointe Magazine
To do this, all you need to do is pull back the fabric around the shank so that is it exposed and trim it to where your arch is the deepest. You'll also want to make sure to shave the end of the shank down so it is smooth. When you're done, you'll have a shank that conforms to your foot better and looks better on your foot!