nvidia – Configuring 2-monitor setup

I was using Ubuntu 20.04 and liked it fine. It handled my 2-monitor setup properly. I wanted an app that is only available for 18.04, so I just installed 18.04 (replacing 20.04). After installation, it was handling the 2 monitors correctly. When I tried to open Notepad++, it said there was not a driver available that could open a new window, so I installed a new driver. I let Ubuntu choose the appropriate driver for my video card. Now the second screen is just a duplicate of the first screen. How can I change the setup parameters of my video card driver (NVIDIA GeForce GTX 1060 WINDFORCE OC 6G)?