Yes, but it's a bit complicated. If you filed 2 returns as "married filing separately" and want to change to "married filing jointly", then you pick one of the returns, start to prepare an amended return, and add the details from the other spouse. When you file the amended joint return, both separate returns will automatically be canceled, you don't do anything special to cancel the other separate return.
However, there are some details about "adding the other spouse's information" that are more complicated than doing it automatically, to make sure the income tax and refund are correctly calculated. Some instructions are here.
https://ttlc.intuit.com/turbotax-support/en-us/help-article/amend-tax-return/amend-married-filing-se...
This answer has been verified for accuracy by an Intuit expert employee
