I have an excel with field called sales% in my excel in which all its values will be in % but when i open the same excel in Nprinting template the values are not in % rather its like 0.342648840867748.
First of all, you cannot change formats if you are exporting a pivot table using the 'tables' object in NPrinting Template editor. The source table must be a straight table.
Once you have a straight table, expand so you can see all the individual fields in the template editor.
Then you can deselect 'keep source formats' for each field value that wish to apply specific formats to then and apply your own formats as needed either leveraging the custom formats in MS excel or using the format property for each field value.
To expose the field 'properties' just right click on the field value under the expanded chart object in the NP designer template editor and click 'properties'
For more information regarding your requirement, check the following help pages: