What major should I choose if I would like to go to chiropractic school after my first 4 years?

Chiropractic schools generally require coursework in the liberal arts and in sciences like physics, chemistry, and biology. So I think you can pick whichever major you want. No matter which major you choose, you'll set yourself up best for doing well in Chiropractic school if you take a decent amount of courses in the sciences while you're in college.

That being said, you should definitely look at the admissions website of a few specific Chiropractic schools you're interested in, and see what they say are the requirements for admissions are - because you won't be eligible to apply if you don't meet the requirements. For example, here is the website for University of Bridgeport's Doctor of Chiropractic DC Degree Program that lists out the requirements: https://www.bridgeport.edu/academics/schools-colleges/school-of-chiropractic/chiropractic-dc/admissions-requirements

This is also a great site from the government that gives a lot of information about being a Chiropractor! https://www.bls.gov/ooh/healthcare/chiropractors.htm

Last thing -- pre-med isn't actually a major (don't worry, common mistake), it's actually a "track". People who are pre-med are taking courses that will allow them to meet the requirements to apply to medical schools, but they can choose ANY major they want (even a non-science major) as long as they meet all the requirements for med school. You'll want to figure out what your pre-chiropractic "track" will look like based on the requirements of chiropractic schools.

Chiropractic school has nothing to do with actual science or medicine, so you can pick whatever major you want.