Look for a two or three-pin header labeled or "CLR1" . It is usually located near the bottom right corner, next to the front audio header. There is no button. You have to move a jumper cap from pins 1-2 to 2-3 for ten seconds.
Have you wrestled with an Acer MG43M? Did you ever find the hidden BIOS menu? Let me know in the comments below. Acer Mg43m Motherboard Manual
Spoiler alert: You aren't going to find it. Look for a two or three-pin header labeled or "CLR1"
If you are reading this, you have likely just picked up a used Acer Aspire desktop, or you are trying to resurrect a dusty tower from the back of your office closet. Inside, you spotted the model number MG43M printed on the green PCB. Acer Mg43m Motherboard Manual