See: Help:User rights

If you're also a bureaucrat, see Help:Bureaucrats' how-to guide

Where's the dashboard? I got the roles from adoption request by the way

See: Help:Admin Dashboard as it has an image showing the location

I believe you can also do it from sidebar on their user page under Change User Groups

Ex:

If this is still needed: Admin dashboard is on the right(at least on my laptop) I think, its after clicking the three dots which appear near the number of pages it says and a bunch of other buttons, hover over the three vertical dots and its the third one down, after clicking 'Admin Dashboard' go to the community section (second section) and the second button 'user rights' is what you should click, afterwards copy and paste the user and checkmark whatever role you want to give

Hope this helped at least someone