Problem fixed using the below code and adding the as col1 highlighted
--File 2 OPTION.txt
SELECT DISTINCT
B12.MODLN_USC_C + ';' +
LEFT(ENT_ENTITY_C, 1) +
SUBSTRING(ENT_ENTITY_C, 3, 1) +
SUBSTRING(ENT_ENTITY_C, 6, 1) +
SUBSTRING(ENT_ENTITY_C, 4, 1) +
SUBSTRING(ENT_ENTITY_C, 5, 1) + ';' +
b10Opt.USC_C + ';' +
LTRIM(RTRIM(ISNULL(B10Opt.USC_DESC_X, ''))) as col1
FROM
(select ent_entity_c, modln_usc_c, ent_opt_usc_c
from CDMStaging..mfslb12_entlst
where MKT_C = 'FF' AND ENT_STATUS_C IN ('O','B')) AS b12
INNER JOIN
(SELECT usc_c, usc_desc_x
FROM CDMStaging..mfslb10_elm
where mkt_c = 'FF') As B10Opt
on CHARINDEX(B10Opt.usc_c, B12.ENT_OPT_USC_C) > 0
ORDER BY 1