mac adress reset

I had changed my mac adress for my unban for Steam (Later I now that I could'nt unban from Steam)
but how can I reset my mac adress to original because i cant sign into Xbox live

Google?
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Wow u rich guy
by it for steam(PC) and xbox
And u can try restore ur computer to an earlier date or time idk

but it doesnt really help if you dont know ur previous mac address, i think....