Hello Flutetringby,
version 1.0.2 of the plugin should NOT create the "Input/Output Settings for G'MIC QT" entry in your menu. This was added in later versions of the plugin, which according to my tests (on Windows 8.1 x64) do NOT play well with Paintshop Pro. You probably did NOT download the version 1.0.2 I linked to.
However, the author has just released
version 1.2.1 of the plugin, noting that the PSP incompatibility I mentioned to them in their
Issues page has been fixed now.
I just did a quick test with the x64 variant of that latest version 1.2.1 and it now indeed seems to work well with PSP (I only tested just a couple of Artistic effects). Note that this latest version does add the 2nd entry "Input/Output Settings for G'MIC QT" in PSP's menu. According to the plugin's
Releases history, that 2nd menu entry was added in version 1.2.0... it is there because some G'MIC filters need 2 source images to do their magic (I have no idea which ones tho).
As for installing the plugin, it is just a plain zip file, not an executable exe file (actually there are no executable installers available on the plugin's page). Just d/l the version you want from the plugin's page, and unpack it inside one of the folders you use to keep your PSP plugins (which should be different for PSPx32 and PSPx64).