You cannot change the value displayed in a column conditionally with datagrid. However, you can do this in datagrid2 or a listview. Use a Text widget and make the displayed value using an expression. See here for more information: https://docs.mendix.com/studio/page-editor-widgets-text/#content
In datagrid, you could use the Grid Cell Styler widget to turn the 0 red or bold or create some other visual cue for the user. Link to the widget here https://marketplace.mendix.com/link/component/106254
Hope that helps.