Unfortunately, unless you can return the defective can you have.
Though the inner workings of an aersol can are simplistic in mechanics, they are not servicable. You're better off returning to the retailer or just tossing it in the trash to avoid a risk of being injured.
Having managed a hardware store, I can tell you stories about customers who tried to save themselves a few bucks by "repairing" the can. Most came in wearing its contents and were lucky not to have blinded themselves.
Contents under pressure are nothing to take lightly. Many of the propellants that are used to "push" the paint out are flammable as well. Many use propane...which will go BOOM under certain circumstances.
We like having you around so please, don't do something foolish...unless you feel your life is only worth $5.