On page SEO for non web developers

Hi, I kinda hate asking on here for everything but everyone is so damn helpful :)

I'm just starting my learning in SEO and enjoying it. I'm using a friend's site as a practice situation, he has a medium size tech company with a terrible website (they do a pretty specific networking with huge corporations...they don't drive sales with the website. That said, people can't even find them they basically don't exist).

He wants me to fix up and will pay me, but I'm not thinking of that side, if I do a good job I'll charge him something later.

Anyway, as I start my journey I see lots of things I know how to fix already, but when it comes to on page SEO I'm a bit confused. I know not all SEO folks have to be great at web design (I intend to learn and already know a bit, I can fix things with a bit of code here and there, pretty minimal)...so what do I do when I see significant on site issues.

I guess I figure: If they have a web designer or access to one just ask them to get it to fix it, but what if they simply don't... someone made the page once and it's sat there since. Do i just hit up fivr and find someone who can make the edits?

Sorry if this seems dumb, just wondering what the standard is, and I guess what the standard level of expertise is/should be. Should I be expect that I should be able to do these changes myself if I'm gonna be any good?

As always, appreciate any feedback.