how to reset Razer Deathstalker v2

You can try via Synapse: click on the "gear"/settings icon on the top right, then go to reset tab -> there will be your keyboard, click on reset button. You can also try this steps, but they doesn't include DeathStalker V2 atm, I assume, that the procedure will be similar to huntsman keyboards: https://mysupport.razer.com/app/answers/detail/a_id/1697/~/how-to-fix-an-unresponsive-razer-keyboard-with-a-hard-reset-or-by-exiting-out