Canon 4050 copier has line down the paper. How do I get rid of it

Take out toner and shake it to clean the toner cartridge
or you need a new drum

Check and see if the black line is on the drum! you will need to drop down the transport assembly then with a flashlight look at the drum to see if the black line is in the same position as on the page. If you see the line on the drum you will have to replace the drum blade! you may want to try and flip the blade before trying to buy one! you will need to make sure that the developer is cammed away from the drum before removing the drum if you try to pull the drum out without camming the developer you will scratch the drum!