sha1() is a PHP function. You could make a PHP file like this below and run it:
echo sha1(substr('abcd1234', 0, 8).'thepassword'.substr('5678cdef', 8));
...where 'abcd1234' is the first 8 characters of the passsalt column, and '5678cdef' is the last 8 characters of the passsalt column.