How to unlock a Prepaid Surfstick?

I have an O2 Prepaid Surfstick purchased in Berlin in September 2015 and I would like to remove the Simlock from it. I believe this is possible after 2 years.

Currently I am in the Czech Republic and I purchased an O2 pre-paid mobile internet sim card, but the Surfstick is asking for a Simlock code.

I have the IMEI code and all information for the Surfstick. Can someone please advise me how to unlock it?

 

Thanks and regards,

Peter H.