How to edit default dictionary

I was wonder if there was a way to edit the default dictionary (NOT the personal word list).

i have a character named Sam and the auto-correct keeps auto-correcting “sam” (all lowercase) to “SAM” (in all caps).
It’s really annoying.

I’ve already tried adding “Sam” to personal word list as well as adding a substitution to turn “sam” into “Sam”. Neither worked.

How can I change this behavior outside of plain turning off auto-correct?