I mistakenly submitted my tax returns as resident alien, how do I update to non-resident alien?

You cannot update your return.  You have to amend to a Form 1040-NR.

Wait until your return is fully processed and you have received your refund or your payment has cleared. You would need to submit both the Form 1040-X and form 1040NR together:

• Download the Form 1040-X from IRS website (see below).  On the front page of Form 1040-X, enter your name, current address, and social security number (SSN) or IRS individual taxpayer identification number (ITIN)
• Do not enter any other information on page 1.  
• Do not complete Parts I or II on page 2 of Form 1040X.
• Enter in Part III the reason why you are filing Form 1040X.
• Complete a new or corrected form 1040-NR.  As TurboTax does not support nonresident forms, click here Sprintax.
• Across the top of the 1040-NR, write “Amended”
• Attach the new or corrected return (Form 1040NR) to the back of Form 1040-X and submit to the IRS.

https://www.irs.gov/pub/irs-pdf/f1040x.pdf  - form

https://www.irs.gov/pub/irs-pdf/i1040x.pdf  - instructions

(See page 6 under Residents and Nonresidents)