TYPES:
BEGIN OF ty_tab,
pernr TYPE persno,
END OF ty_tab.
DATA: tab TYPE STANDARD TABLE OF ty_tab.
DATA wa_tab TYPE ty_tab.
wa_tab-pernr = '00000001'.
INSERT wa_tab INTO TABLE tab.
wa_tab-pernr = '00000002'.
INSERT wa_tab INTO TABLE tab.
wa_tab-pernr = '00000003'.
INSERT wa_tab INTO TABLE tab.
LOOP AT tab ASSIGNING FIELD-SYMBOL(<tab>) FROM line_index( tab[ pernr = '00000002' ] ) .
IF <tab> NE '00000002'.
EXIT.
ENDIF.
WRITE: / sy-tabix, <tab>.
ENDLOOP.
"Retrieve WA where field meets condition
DATA(lw_wa) = tab[ pernr = '00000003' ].
"Retrieve field field meets condition
DATA(lv_pernr) = tab[ pernr = '00000003' ]-pernr.
"Update lines with '99999999' where field meets condition.
tab[ pernr = '00000003' ]-pernr = '99999999'.