To reinstall the OEM you would have to install Windows from the manufacturer’s recovery environment. This may return you to an older Windows version.
If you upgraded to Windows 10 from a previous Windows (7, 8/8.1) then it does show retail even though the license is OEM.
If you clean installed Windows 10 after trialing Linux then the manufacturer’s recovery partition will have been removed so you’d have to contact them to see if they offer a DVD recovery set.
There’s no difference between OEM & Retail other that what I mentioned. It’s just a question of naming - OEM doesn’t give you any extra benefits & tbh usually comes with the PC maker’s bloatware like trial for various AV software.
If this isn’t clear for you then I’m sorry.