Can I change to three year rule?

The 3 year rule or sometimes called general rule cannot be used.  Please see this link for more details.

If you were retied a number of years ago under the 3 year rule then 100% of the annuity is taxable income to you now, and you would need to Amend 2017 to increase your taxable income.

https://www.irs.gov/publications/p939#en_US_201812_publink100094759

I have resolved prior year's mistakes with IRS. Just need to keep from perpetuating the error!!!!

if I had not imported data from 2017 return the program would never know I mistakenly used Simplified Method last year!!

What year did you retire?

6/2016 and recovered my contributions by end of 2017.

If you receive pension or annuity payments from a qualified plan and you aren't required to use the General Rule, you must use the Simplified Method to determine the tax-free part of each annuity payment.  Pub 939. link if answer.

You cannot use the General Rule due to when you retired unless you retired at age 75 or older.