Hi BestieDako
I am Dave, I will help you with this.
1
Rest assured, resetting Windows will not have any affect on activation or Windows licensing, you do not need to worry about that, you will not be asked for a product key.
2
Even if you need to re-install Windows 10 from a bootable USB, activation would be automatic.
Since you previously had Windows 10 installed and activated on that PC during the installation process skip the steps which ask for a product key and select the option 'I am Reinstalling Windows 10 on this PC', and activation will not be an issue, your PC will have a digital entitlement stored on the Microsoft Activation Servers