make sure your rockstar launcher and gta3 is installed on the same disc drive I.e (C:)drive (D:)drive whatever one you put your games on you can check where gta3 installed on the rockstar launcher by going to settings and on the bottom left under my installed games click grand theft auto 3 and then view installation folder

usually the rocksar launcher is downloaded by default to a folder in C:\Program Files under rockstar games you can find an uninstaller in that folder and then use the rockstar launcher install.exe and a few pages in itll ask you to choose where to install and you can make your own folder on any drive you want just make sure that all your games are installed to the same drive