In 2018 I was a 1099 contractor; based on that Turbotax calculated my estimated taxes. In 3/19 I changed jobs; I am now a W2 employee. How do I recalc my estim taxes?

To prepare estimates for next year you start with your current return, but be careful not to change anything.  If you can't get back into your return, Click on Add a State to let you back into your retun.

You can just type W4 in the search box at the top of your return , click on Find. Then Click on Jump To and it will take you to the estimated tax payments section. Say no to changing your W-4 and the next screen will start the estimated taxes section.

Or Go to….
Federal Taxes or Personal (Deskop H&B)
Other Tax Situations
Other Tax Forms
Form W-4 and Estimated Taxes - Click the Start or Update button

This was not my question.

That is how to go to the estimated tax section to prepare estimates.  You can adjust them there for 2019.  Ok then just pay the first quarter one and ignore the rest.  Or don't pay any.  Or send in about 20% of your 1099 Net Profit to cover the self employment tax.