alert before one months date of expiry

SELECT *FROM YourTable

WHERE

(CASE

WHEN DATEDIFF(MONTH, GETDATE(), LicenceExpiryDate) >= 1 AND DATEPART(DAY, LicenceExpiryDate) >= DATEPART(DAY, GETDATE()) THEN DATEDIFF(MONTH, GETDATE(), LicenceExpiryDate)

WHEN DATEDIFF(MONTH, GETDATE(), LicenceExpiryDate) >=1 AND DATEPART(DAY, LicenceExpiryDate) < DATEPART(DAY, GETDATE()) THEN DATEDIFF(MONTH, GETDATE(), LicenceExpiryDate) - 1

END)>0