SEO for other businesses

Im starting out in SEO i wanna optimize small business websites near me but im actually not sure how the process goes. Im currently doing the online course that google has for marketing and ive VERY confident in how search engine works but how do I approach a business who has a website? Like do i call and ask them about what software/ website they used to create their own website and get their login info to make adjustments for their website? Or is there another website im not familiar with that helps me make changes without getting all their private login info on their website?