Even if the driver is installed, the software might be looking at the wrong port.
If your Geomaster GM2020 connects via a USB cable but acts as a "Serial" device (common in surveying instruments), it likely uses a generic USB-to-Serial chipset. The most reliable drivers for this are the Prolific or Silicon Labs drivers.
Sometimes you do not need a separate driver. The GeoMaster GM2020 often works with: geomaster gm2020 driver download link
If you install the full data collection software for your device, the driver installs automatically.
90% of GeoMaster GM2020 units use the Prolific PL-2303 HXD chipset. Even if the driver is installed, the software
How to get it:
Go to prolific.com -> Support -> Downloads -> PL-2303 Driver Installer. Look for the "PL2303HXD (Rev D) / HX (Rev C) / EA (Rev A)" driver.
If the official site has vanished, the Internet Archive is your best friend. If you install the full data collection software
Once you have downloaded the file from the links above, follow these steps:
Since no single universal "GM2020" driver exists, you must download the driver based on the Chipset Hardware ID.