The easiest way to do this is one of the following two ways:
Click the Multi-Instance Manager icon, or hit
CTRL+8 in NoxPlayer (see picture below).
Search Windows directly for the program and launch it.
This is done by clicking the Add emulator-button and selecting New emulator. Note: you may wish to clone an existing instance if you want the same apps installed (e.g. if you are setting up a bot farm for the same game).
Repeat steps 2 and 3 to create and boot as many instances as you like.