Assuming you have already filed your return, you can amend and add Form 8936 to your return. How do I amend my tax return?
IRS Document Upload - After you amend, and depending on instructions in the letter, you may be able to upload to the IRS without e-filing it.
It is true that you must file Form 8936 when you file your tax return for the year in which you take delivery of the vehicle. This is true whether you transferred the credit at the time of sale or you’re waiting to claim the credit when you file. Per the IRS