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I can't tell you step-by-step how to start a credit repair business, from home or not, because I've never done it and I don't know that business. I can however point you to a lot of very good general information about starting your business.
You asked this question at Entrepreneur.com, which is the best place to start looking. Go back to the homepage and look at the sections to see how much is available on starting your business.
There is a major "starting your business" section at www.bplans.com. That one too is marked from the homepage.
For live people, get in touch with the nearest Small Business Development Center (SBDC). You can find a list at bplans.com/sb/. These are funded by federal, state, and local money and usually provide great information for relatively low prices.
As for your specifics, find someone who's already in that business, somebody whose advice you can trust, and ask them to help. Specifics are very important, there is no substitute for experience, and usually there are people somewhere who would be willing to help you. Sometimes what it costs is the price of lunch. Do some web searches too. Don't be afraid to search for "starting a credit repair business" because even though you'll get a lot of useless leads, you may find something that helps. Keep asking questions. Don't start the business until you're comfortable with what you can reasonably expect. Finally, my area of expertise, do a business plan. You'll be glad you did.