This page contains information that may help if you encounter an issue with Regolith Linux. If your problem isn’t already here, kindly file an issue and describe your problem.
Regolith is installed using Debian packages. By design, a package will fail to install if by installing it would overwrite existing files on your system. So, if you have already installed (either via package or compiled from sources) i3-wm, rofi, gnome-flashback, or compton, you will not be able to install Regolith without moving or removing them. To remove them, run
sudo make uninstall from the source directory, or use
sudo apt remove <package> for non-Regolith debian packages. Once removed try installing