Last night I inadvertently ordered 2019 Premier Deluxe via CD/Download rather than online as I have done since 2011. Do I have the ability to switch to online?

The TurboTax desktop CD/Download editions and the TurboTax online editions have different price points. 

Go to this TurboTax website to request a refund for the software purchased from TurboTax - https://support.turbotax.intuit.com/forms/refund-request.jsp
Use this TurboTax website to check your orders and payments -
https://turbotax.intuit.com/personal-taxes/cd-download/order-status/

Or contact TurboTax customer service/support use their contact website during business hours. If the problem concerns any type of refund for fees, use the key words billing issues and do Not use the word Refund or you will get a phone number for tax refunds.

Use this website to contact TurboTax support during business hours - https://support.turbotax.intuit.com/contact/
Support can also be reached by messaging them on these pages https://www.facebook.com/turbotax/ and https://twitter.com/TeamTurboTax