Are you looking for something like
WITH Mnths AS
(
SELECT DATENAME(Month, DATEADD(Month, M - 1, 0)) MName
FROM
(
VALUES (1), (2), (3), (4), (5), (6), (7), (8), (9), (10), (11), (12)
) T(M)
)
SELECT REPLACE(RIGHT(T.V, LEN(V) - CHARINDEX(M.MName, T.V) + 1), '\', ' ') Result
FROM Mnths M JOIN
(
VALUES
('\192.168.50.100\folder\march\filetypeA\filenameB'),
('\192.168.50.100\folder\August\filetypeA\filenameB')
) T (V)
ON T.V LIKE CONCAT('%\', M.MName, '%');
Which will returns:
+----------------------------+
| Result |
+----------------------------+
| march filetypeA filenameB |
| August filetypeA filenameB |
+----------------------------+
Demo