I have a penasonic TC-21PM50R [crt]almost 4 years old Tv. Now some chanels are locked.[childlock] I don't know how to unlock it

I have a penasonic TC-21PM50R [crt]almost 4 years old Tv. now some chanels are locked.[childlock] I don't know how to unlock it

If you still have the owner's manual, check in there for a master reset. I looked on Panasonic's website, but couldn't find that model so I couldn't find anything about that model. I also searched through Google and didn't find anything helpful.