For convenience, we've copied some of the information from the College Board/AP website below:
If you’re homeschooled or you go to a school that doesn’t administer AP Exams, you’ll need to arrange to take exams at a local school that does administer them.
Your first step is to search the AP Course Ledger. The AP Course Ledger is the official, up-to-date, comprehensive list of schools that have passed the AP Course Audit. You can search by country, state/province, or city to find a school where you might be able to test. After finding schools near you that offer the course or courses you want to take exams for, do an internet search for the school’s main phone number. Then call and ask to speak with the school’s AP coordinator to ask if the school is planning to allow homeschooled students to test there this year.
We recommend you do this as early in the school year as possible. Note that schools may have their own local deadlines and policies for receiving requests from outside students to test at their school--particularly this year during the ongoing pandemic—so you’ll want to give yourself as much time as possible to contact schools.