Explanation
Dataverse includes a web application tool called Import Data Wizard. You use this tool to import data records from one or more comma-separated values (.csv), XML Spreadsheet 2003 (.xml), or text files.
Use transformation mapping to modify data before importing it. For example, split a full name that is contained in the source file into a first name and a last name to match the target columns for a table.
Note:
To implement data import, you typically do the following:
Create a comma-separated values (CSV), XML Spreadsheet 2003 (XMLSS), or text source file.
Create a data map or use an existing data map.
Create a comma-separated values (CSV), XML Spreadsheet 2003 (XMLSS), or text source file.
Create a data map or use an existing data map.
Associate an import file with a data map.
Upload the content from a source file to the associated import file.
Parse the import file.
Transform the parsed data.
Upload the transformed data into the target Dataverse server.
Reference:
https://docs.microsoft.com/en-us/powerapps/developer/data-platform/import-data
https://docs.microsoft.com/en-us/powerapps/developer/data-platform/add-transformation-mappings-import