The steps to reset an HP 1810-24G smart managed gigabit switch are as follows:
1. Using a paperclip, simultaneously press the Reset and Clear buttons.
2. Release the reset button, while continuing to press the Clear button.
3. When all three mode LEDs (Act, FDx, and Spd) begin to blink, release the Clear button.
Once the switch completes the self-test, the switch will be reset to factory defaults. The default IP address will be 192.168.2.10 and there will be no password.
Source:
http://coderzen.com/2013/06/04/how-to-reset-a-hp-1810-24g-to-factory-defaults/