Can you submit a Form 8888 after filing your taxes?

I filed my taxes thought TurboTax and got them approved by the IRS. I opted for my tax refund to be direct deposited into a bank account.

 

Today, I realized I forgot to look into Form 8888, by using my return to be put into a savings bond. I didn't see this option offered when Turbotax was asking about where my tax refund was to be put.

 

Would I still be able to do this even after I submitted my taxes and have it accepted by the IRS (this was an extension return)? If so, how could I do this?