It is difficult to answer your question when you didn't list the text of the diagnostic and you didn't say which module you are in (Individual, Corporate, etc.). 

With regard to Form 8621 entry (assuming this is an Individual tax return), have you tried going into the Other Taxes input (Screen 45.3 in Lacerte), scrolled down to the Other Taxes section, and then made entries into the Form 8621 overrides?

If you are just asking where to enter ordinary income, take a look at the Miscellaneous Income input (Screen 14.1), and see the Other Income entry.

Note: there is no need to "clear" this diagnostic as it will not block electronic filing. It is not designated as an e-file critical diagnostic. You can check the box next to the diag to strike a line through it, for your own reference purposes.