Since there is no RetroPie OS for Raspberry Pi specific to CrowPi2 being posted by Elecrow, you can follow the instructions below to flash a new MicroSD card with the RetroPie OS for CrowPi2.
Insert a new MicroSD card (32GB or larger) with a MicroSD Card USB Adapter into a USB port of the Raspberry Pi.
Launch the Raspberry Pi Imager app (Menu > Accessories > Imager).
Click CHOOSE OS.
From the Operating System list, choose Emulation and game OS.
Choose RetroPie
Choose the appropriate version for your Raspberry Pi model.
Click CHOOSE SD CARD.
From the SD Card list, choose your desired SD Card for flashing with the selected image.
Review your selected OS and SD Card and then click WRITE.
Click YES, when you are ready to start the flashing process.
After flashing has completed, click CONTINUE and close the Raspberry Pi Imager app.
Next, you will need to edit the config.txt file in the newly flashed RetroPie SD Card before it is suitable for use with the CrowPi2.
Unplug the MicroSD Card USB Adapter with the RetroPie SD Card and then plug it back in for it to be mounted in the system.
Open a new Terminal (Ctrl+Alt+T).
Edit the config.txt file in the RetroPie SD Card with your favorite text editor (Ex. nano). Type
sudo nano /media/pi/boot/config.txt and press Enter.
Cut and paste the following statements to the end of the file.
Press Ctrl+X, Y and Enter to save the file and exit the editor.
Finally, your RetroPie SD Card is now ready for use in the CrowPi2. Shutdown the system, then unplug the power and replace the system SD Card with the RetroPie SD Card.
Since there is no RetroPie OS for Raspberry Pi specific to CrowPi2 being posted by Elecrow, you can follow the instructions below to flash a new MicroSD card with the RetroPie OS for CrowPi2.
sudo nano /media/pi/boot/config.txt
and press Enter.