Hi Naresh,
There are 2 options.
1. Static label change.
You can change the text in the i18n language translation file.
2. Dynamic lablel text change by SO type or something
You can change the UI code and add dynamic logic by Java Script.
Please refer this how to guide for downloading and uploading the UI code.
How to Guide: SAP Fiori Extensibility - Addind Custom Fields in UI
Regards,
Masa