Kinda strange question, but how to ask SEO clients for access to their website?

I am planning on starting SEO soon. I think I have more than enough skills to rank for local search terms. However, I have business plan in mind, to offer SEO service to clients who are on page 2 or 3.

How should I approach them about getting access to website? Those are lawyers,dentists,shops... 90% of them I think only hired someone to make website and left it like that. I really doubt they even know what is SEO, and their hosting login info. I would need this for on page SEO.

This might be really dumb question, but I really don't know how should I proceed, I haven't found any answer on forums.

Try to figure out who is hosting the site, which you can usually determine with a quick whois lookup. See what DNS nameservers they're using - ie. if it's nsXXX.hos*tga*tor.c*om then you'll know they're with that company and can say "forward me the emails from <insert_company>".

You can also put together a quick little onboarding doc in Word or GDocs that asks all these questions - and usually they'll have a semi-technical person they can pass it onto who will get those details for you. The fact that they have a website means they worked with someone who at least knew how to install a WordPress theme and they can get you the deets.

Things I ask for as a consultant when onboarding a new client (bare minimum): hosting panel, site logins (ie. wordpress admin), analytics + webmaster tools (if setup), domain registrar login, and contact info for the person who made/updates the website.

Asking a business for access to their site is easy once they want you to work for them, you obviously need access to the site if they hire you.

I think the hardest part in your senario is getting the business or lawyer etc to hire you in the first place.