In general, the depth of the ink into the paper determines the success of the removal process. That and the thickness of the paper.
Examine the area. I usually start by scraping the ink with my specially designed book repair knife. It is rounded at the tip and has a long bevel that is good for other applications. Scraping with a pointy knife makes it too easy to cut through the paper.
If the ink is fairly shallow the best solution may be to sand the entire side of the text-block. Use 100 grit then higher number grits up to 320 or so.
Be sure to clamp the text-block tightly before sanding.
If the inked area is deep you may like to excise the inked area again using the book repair knife.
There is no bleach or product that will remove the ink without damaging the paper even more.
After excising the area you can sand it to even it out. The reason to scrape it first is that sanding can sometimes spread the ink around so it just looks even messier.
Without the specific book repair knife you could grab a butter knife and sharpen the rounded end yourself to get a similar effect. Or sharpen a micro-spatula.