Can I amend a tax return I filed in Oct 2016?

The IRS will accept an amended return up to 3 years after the date you filed the original return or within 2 years after you paid the tax due on the return, whichever is later.

Below are steps for amending a 2016 return:

https://ttlc.intuit.com/replies/5114064

In my situation the "original return" was the return filed in October 2016, correct? In other words: my deadline to amend is Oct 2019? Thanks

Yes