Welcome to the forum joeltj
When really that is not easy to do if you have forgotten it, you need to reset the stb back to default so I suggest you search for the master reset pin.
I can only suggest searching the forum for the word master and reading all the threads.
It may be worth trying the Humax std one
select menu,installation,status,ok,press red,green,yellow,blue,white and 0 buttens simultaniously.then press ok.