You'll need to know exactly how many credits you still need, so you can be sure to enroll in the right type of program. Contact your former high school and request a copy. Every state offers a variety of high school completion programs suitable for adults. Do an online search and check with local community colleges to find a program that meets your needs. In most cases, adult high school diploma programs are free. You may need to fill out an application before the stated deadline in order to make sure you can attend the classes you want to attend. When you enroll, you will probably be set up with an advisor, who can look through your transcript and help you make sure you get the credits you need. Each program has requirements that differ slightly according to state law. Work with your advisor to lay out a plan to complete all the credits you still need. Depending on how many years of high school you previously completed, this could take just a few months or several years. Upon completing your program, passing your classes and meeting all the requirements, you'll be able to graduate with a high school diploma.

How would you rephrase that briefly using Chinese?
找到你的高中成绩单复印件。 找一找你附近的成人项目。 报名参加项目。 完成课程的要求。 收到你的文凭。