The first step towards repairing your damaged credit would be to find out what factors caused the damage to your credit. A bad credit could be due factors such as: 1. Not paying the bills on time 2. Having high credit utilisation ratio on your credit card 3. Delinquencies 4. settlement 5. foreclosure etc. 

Repairing your damaged credit immediately may not be possible as it involves a lengthy process. To start with, you can review your credit report and identify the negative issues on it. Improve your credit history by making payments on-time consistently. Clear the past dues if you have any with the lender. This could improve your credit score considerably. 

If you are unable to resolve your credit issues on your own, you can also seek the help of a credit repair company who guides you through the process until you have a improved credit score.