Really, you are asking two different questions. Entity Framework is not a database administration tool and as such does not have any functionality for directly loading data from a spreadsheet.
If you research each part of your question separately, you might have more luck.
Seeding data with Entity Framework
Reading Excel Files with C#
Reply to comment:
if (!context.PostalCodes.Any())
{
IEnumerable<PostalCode> postalCodes = ReadPostalCodes();
foreach(var postalCode in postalCodes)
{
context.PostalCodes.Add(postalCode);
}
context.SaveChanges();
}
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solved Entity Framework populate entity at starting [closed]