If you're just hardcoding the values outside the subquery, you don't need a subquery to return the 2 rows, just do this:
SELECT '' ORG_UNIT, '' EMPE_ID, '' FAM_NAME, 'Used' AS TMS_TYPE, -1 AS QTY
FROM TABLE
WHERE COMP_CODE = 'TEST'
AND (DETL_REMK = 'Rest Day'
OR SHFT_CODE = 'WK_PH')
AND RSRV_DATE_1 IS NOT NULL
AND RSRV_DATE_1 BETWEEN @TR_FR AND @TR_TO
AND EMPE_ID = 'TEST'
GROUP BY EMPE_ID,
RSRV_DATE_1
The issue here is you're not referencing any columns from your table, just using it to produce an amount of rows. Please share the full issue and code, as I'm sure there is more to this that what you're asking.