To adjust the words that are in the spell checker's dictionary, first open a new cert, type a misspelled word into a field and click on Check Spelling:
You will see the Spelling dialog appear, as below
Click on Options to open the Spelling Options dialog:
Then click Edit in the "Edit custom dictionary" section to access the custom dictionary:
Adjust the words in the dictionary as needed, then click OK twice to return to the Spelling dialog.