How to delete Field Mapping in Civicrm ?
In order to delete Field Mapping in Civicrm goto Administer -> System Settings -> Import/Export Mappings from the menu, there you can find all existing mappings and you can delete unwanted mappings there. Refer to the screenshot below.
Import/Export Mappings provide a way to save specific imports or exports. CiviCRM allows you to save the field mappings you create during an Import or Export process so that you can reuse them. This is useful if you need to repeatedly import data from another application or export data for a regular report. You create and modify these mappings during the Import or Export process. You can rename or delete mappings you have saved here.
Kindly visit this link for more details.
Hope this helps!!!