If you sell a vehicle after you have filed your Form 2290 Return, you would need to file Form 8849, Schedule 6 in order to claim your credit. You would also use Form 8849 if your vehicle was stolen, destroyed or for any vehicle on which the tax was paid on Form 2290 if the vehicle was used 5,000 miles or less on public highways (7,500 or less for agricultural vehicles) during the tax period.
Form 8849 can be e-filed by anyone who needs to claim a refund, or credit, for sold/stolen/destroyed vehicles, or for vehicles that did not exceed the mileage limit, on heavy vehicle use taxes that have been previously paid.
If you have paid the Form 2290 Heavy Vehicle Use Tax and your vehicle was sold/stolen/destroyed, you can e-file Form 8849 at any time. You just had to have paid the Form 2290 tax first.