1. Press Ctrl+1 to open the Format Cells dialog box.
2. Select the Number tab, and from Category, select Custom.
3. In the Type box, enter the following Custom Formatting syntax:
#,##0.0,;[Red](#,##0.0,);-;

Result:
· Original number: 5,645,625
· The displaying formatting number: 5,645.6

Note:
The number formatting syntax is:
Positive; Negative; 0; Text