By "override a dimension", you mean to type in your desired value instead of using the calculated value?*
The process depends on your NX version, but for NX 8.5 I think it was Edit -> annotation -> text, pick dimension, enter new text.
*This is considered a bad practice if you are changing the dimension value and should be avoided. If you are creating a tabulated dimension (dim A, see table) this is OK. If your drawing has to pass some automated checks, this process will probably be flagged as an issue.
and , there is a very old option ( still brilliant function!) to check for dimensions w manual text.
Information - Other - Object specific - dimensions w manual text
Dimensions with manual text will then highlight.
Regards,
Tomas
The more you know about a subject, the more you know how little you know about that subject.