Unfortunately, TurboTax no longer sells or supports the 2014 TurboTax software. Even if you could purchase the software from someone else, you may not be able to get the updates to the program since TurboTax no longer supports that year.
You can manually prepare an amended return & mail it in. Generally, for a credit or refund, you must file Form 1040X within 3 years after the date you timely filed your original return or within 2 years after the date you paid the tax, whichever is later.
The Federal amended return (1040-X)
https://www.irs.gov/pub/irs-prior/f1040x--2014.pdf
1040-X Instructions
https://www.irs.gov/pub/irs-prior/i1040x--2014.pdf
If you need to amend a state return, you can check your state's website for their 2014 amended form.
