It some what depends on where you live, but typically CPR classes are held by the Red Cross or by local EMS or Fire Houses. I will share a link below where you can enter your zip code / location and get information about CPR classes in your area.

It looks like there may be online classes, but I would highly recommend going to an in person class if you have never been certified before. Be aware that the breaths and reps change by age and often change, so certifications are only for a few years. It's possible that your local YMCA may also have classes (or other similar organizations).

Hope this helps! Wish you well.
https://www.redcross.org/take-a-class/cpr