My panasonic TV th46pz80b has a black line down 1 side how can I get rid of it

This depends. Is this something on all channels? Or just some. If it's some, you could try playing with the Format button, but since you say it's only on one side, it is hard to say.

Chances are though, that if this is on all inputs, and all channels, that there is something wrong with your TV and it is next to impossible to diagnose an issue with a TV without seeing it in-person. Expect to pay around $100-$200 for an in-home diagnostic.