It’ll probably be like any other type of research search. Be polite in your email. Explain who you are, why you’re writing to them, and why you’re reaching out to them specifically (if there’s specific research they have done). Keep it short and concise and ask if they are willing to correspond with you via email or phone.
You say you’re an incoming freshman so I’m assuming you’ve never had classes with these professors or met them in person. Sending cold emails might not yield that high of a response (do you have a student email yet?) so you can also see if there are webpages for research labs on your school’s individual departments. If there’s a lab manager listed, they might be a better person to contact since the PI usually doesn’t do all the clerical work of finding student volunteers. Also keep in mind that some research labs might not be doing much with Covid.
Feel free to PM me a draft of your email if you want to run it by someone. I used to work in a clinical research lab and I did 4 years of research in college.