How do I re-pair/reprogram a key to my 2008 BMW 120i after battery has been recharged?

One key lost charge after a month of non use. Is now recharged, and starts the car, but keyless entry buttons don't work.How do I re-pair/reprogram a key to my 2008 BMW 120i after battery has been recharged?You gotta get the key programmed at the dealer, or a tech-shop. They hook it up and program any special features you would like.