for Blazor WASM its a standard file upload (<input file>) to the asp.net core webapi. You should be able to find lots of asp.net core examples.
https://learn.microsoft.com/en-us/aspnet/core/blazor/file-uploads?view=aspnetcore-5.0&pivots=server
if you meant to parse the xls sheet in blazor then you need an excel parser that runs in blazor. find a .netstandard 2.0 library version that supports memory streams to read the excel file. if you can not find one, there are javascript ones you could use.
note: with WASM blazor you need to careful of the file sizes