I want to edit a costum field text, like example Unit Price i want to name it to Final Price
Unit price is not a custom field. it is an in-built column in Manager.
it can be changed only by theme customization.
if you are not familiar with liquid coding, please hire a local programmer.
read this guide for ideas https://www.manager.io/guides/7877
also search the forum as there have been many topics discussed regarding the same.
if you want to edit a custom field, you can edit the custom field title and contents under Settings.