what have i gone and done,,,please help

Good evening all

Can someone please help with my problem

Thinking i was changing user access to my external hardrive to my adavantage for security reasons, ive ended up with access denied,, in the properties window then on the security tab of my external hardrive i edited(like a idiot the users who could access it, but know I cant access it and no security tab is visible in the properties anymore, I know that its most likely ive removed my access privlege like a twonk but does anyone know how i can return to its original settings

thanks in advance