So in 2014 I started using the piano to produce income.
Several things here.
First, you flat out can't use TurboTax to file or amend a tax return prior to 2016. That's because TurboTax only supports their software for the current tax filing year and three years back. So even if you get the program for 2014/2015 you will not be able to get the "REQUIRED" corrections and critical updates for it, and TurboTax will NOT honor their 100% accuracy guarantee on the 2015 program or earlier.
Second, if amending a return prior to 2016 shows that you get additional refund money, the IRS will not pay it. There's a three year statute of limitations on refunds. But if you owe the IRS, you are required to pay it regardless of how far back it is up to 10 years. Any additional tax owed has to be paid with interest too.
Third, since you started producing income in 2014 that means you would have reported that business income on SCH C as a physical part of your personal 1040 tax return. If you haven't be depreciating the piano since then, that's a problem that "you" can't fix by yourself.
Because it's been 6 years that you've been self-employed and using the piano as an income producing asset that you did not depreciate but should have, you need to include IRS Form 3115 - Adjustment to Accounting Method, with your 2019 return to correctly fix this.
The 3115 is "NOT" simple by any stretch of the imagination and requires professional help. That's why TurboTax does not include the 3115 with any version of the program. This is particularly important if your state also taxes personal income. So please seek professional help from a licensed, qualified, certified CPA that is legally licensed and registered to operate in your state.
