The Reset can be found on all MikroTik devices, this button can be used to put the device into Etherboot mode. You can read about all possible modes that the Reset button can put your device into by reading the Reset button manual page. An easy way to put a device into Etherboot mode using the Reset button is by powering off the device, hold the Reset button, power on the device while holding the Reset button and keep holding it until the device shows up in your Netinstall window.

Quelle: Etherboot Manual