This article is from the Amiga CD32 FAQ, by Stuart Tomlinson with numerous contributions by others.
A: Connect an Amiga mouse into controller port 2, hold down both mouse buttons, and press the reset button. You'll be given a boot menu where you'll be able to choose either PAL or NTSC. If you have a keyboard then you can press any key to switch the boot menu between PAL and NTSC so you can see what you're doing.
This is useful for NTSC CD32 owners who want to run games that use the PAL area of the screen.
Multisystem TVs connected to any video output on or 1084s connected to the S-Video output will work.
TVs/monitors connected to the CD32 through the French CD32's or SX-1's or CD32x's or TP9's (see diagram at end of FAQ) RGB connector will also work fine.
TVs/monitors connected to the CD32 through the composite or S-Video outputs won't work though. The problem is that the PAL colour signal is still sent at the NTSC frequency.