TRYING TO USE AN OFFSET STATEMENT IN MY SELECT

I am trying to use an offset in my select but it says the offset is the same length of the field. Basically what I want to do is remove the 1st 3 characters form the one field and have the last 3 be moved into the field. They are of different length but I thought the offset would take care of that. here is the code

LOOP AT DATA_PACKAGE.

SELECT AC_DOC_NO

DOC_ITEM

PROFIT_CTR

INTO TABLE T_AZFIG

FROM /BIC/AZFIG_O5100

WHERE

AC_DOC_NO = DATA_PACKAGE-AC_DOC_NO AND

DOC_ITEM = DATA_PACKAGE-ITEM_NUM+3(3).

ENDLOOP.