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.