Question: how to get the credit history back to normal once it is bad? 

Answer: get a small limit credit card, maybe one with a $500 limit, I suggest a gas card. All month long use it to buy gas then when the bill comes pay the balance off in full. You won't get charged intrest and if you use your gas card to buy gas you get cashback bonuses usually. By paying off your balance each month you're adding more points to your FICO score. It may take 6mos. to a year (depending on how bad you messed up your credit) but it's the quickest way to get a better score.
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