Error on an .rpm installer

So far the OS has been amazing for gaming on my Legion Go. I've been testing it because I see it a solid option to get away from Windows. Since I want to use it as a PC/Console hybrid I installed expressVPN. I also wanted to test the drawing software Krita, I have an XPPen Drawing tablet I wanted to use. But everytime I try to install the tablet drivers for Fedora, from an .rpm file, and I get a GPG signature error. It's been a while since the last time I used linux. For some reason the dnf remove and yum uninstall commands, can't uninstall the expressvpn app, I get an error that says Not implemented yet. So. As I understand it, when a new rpm is installed, it seems that every package is updated. Is there a way to add a certain app to some sort of list to exclude it from this process? Or is there a way to fix the issue I am having with the GPG signature of the expressvpn app?