You can include a second IF within the first one so that it functions as though it is testing for a second case if the first case does not match.
=IF(<first case>, <first case matched> ,IF(<second case>, <second case matched>, <no matches>))
In your case,
=IF(ISNUMBER(SEARCH("dba",A1)),"dba",IF(ISNUMBER(SEARCH("bpi",A1)),"bpi",""))