Trying to amend 2019 return to fix TT error on married filing separately default to "someone can claim you as exemption" ?

You will need to amend your 2019 return using a computer.  

In the information section edit your name and check the box Someone can claim me as a dependent if another person can claim you.  If another person cannot claim you, then uncheck the box.  

This does not affect your married filing separately status.  if you were legally married on December 31, 2019, then you can file as Married Filing Joint, Married Filing Separate, or Head of Household if you had a dependent that lived with you all year, that person made less than $4,200 in 2019, and you provided more than 1/2 of their support.

How to Amend