Call the Code Enforcement Officer who sent you the letter, the number will be listed on the Notice of Violation.
Find out how to correct the problem and do so promptly.
You can ask for additional time provided you are making progress on the violations. Some problems are serious and correction must not be delayed. Remember to get proper permits that may be required for some repairs, if need be.
If you are unwilling to take prompt action to correct the problems, there are several possible consequences you may face such as fines and penalties.