The IRS , in Notice 2015-3, establishes procedures for claiming the $0.50 credit for alternative fuel sold or used in calendar year 2014. The notice released on January 16 indicates that a single one-time claim for all alternative fuels should be made no later than August 8, 2015.
Claims should be made using Form 8849 (Claim for Refund of Excise Taxes) with accompanying Schedule 3 (Certain Fuel Mixtures and the Alternative Fuel Credit), and claims should cover the whole year. The notice states that taxpayers who filed protective or anticipatory claims in 2014 must refile their claims; the IRS will not consider the previous claims perfected by the extension of the tax credits. Claims for 2014 may be submitted as early as January 16, 2015 but February 9, 2015 is the official start date for filing such claims and the date that will be used for determining whether the IRS owes interest on any late payments to taxpayers.
To file a claim, a person must be a registered alternative fueler. If you have not filed claims in the past, then you are most likely not registered, and may not be able to claim the credit and registration with IRS can take up to a year.
Detailed info can be found HERE.