How can I read an Excel file from presentation server?

You can use the Function module ALSM_EXCEL_TO_INTERNAL_TABLE to read the Excel file into the internal table of type alsmex_tabline. From this internal table you can fill the target internal table.

TYPES:
 BEGIN OF ty_upload,
   field1 TYPE c length 12,
   field2 TYPE c length 12,
   field3 TYPE c length 12,
 END OF ty_upload.
 DATA it_upload TYPE STANDARD TABLE OF ty_upload WITH DEFAULT KEY.
 DATA wa_upload TYPE ty_upload.
 DATA itab TYPE STANDARD TABLE OF alsmex_tabline WITH DEFAULT KEY.
 FIELD-SYMBOLS: <wa> type alsmex_tabline.

 CALL FUNCTION 'ALSM_EXCEL_TO_INTERNAL_TABLE'
   EXPORTING
     filename    = filename
     i_begin_col = 1
     i_begin_row = 1
     i_end_col   = 3
     i_end_row   = 65535
   TABLES
     intern      = itab.

 LOOP AT itab ASSIGNING <wa>.
   CASE <wa>-col.
     WHEN '0001'.
       wa_upload-field1 = <wa>-value.
     WHEN '0002'.
       wa_upload-field2 = <wa>-value.
     WHEN '0003'.
       wa_upload-field3 = <wa>-value.
   ENDCASE.
   APPEND wa_upload TO it_upload.
   CLEAR wa_upload.
 ENDLOOP.