when is the due date for amending 2017 return

[Just-Lisa-Now-]

Are you asking when the last day to file an amended return for 2017 that has a refund? 

IRS says:

Generally, for a credit or refund, you must file Form 1040-X 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.