Give this a try: https://www.katieandemil.com/t-sql-first-day-of-previous-month?tab=article
put these in variables:
SELECT DATEADD(m,-1, Dateadd(d,1-DATEPART(d,getdate()),GETDATE()))
SELECT DATEADD(m,-2, Dateadd(d,1-DATEPART(d,getdate()),GETDATE()))
SELECT DATEADD(m,-3, Dateadd(d,1-DATEPART(d,getdate()),GETDATE()))
SELECT DATEADD(m,-1, GETDATE())
SELECT DATEADD(m,-2, GETDATE())
SELECT DATEADD(m,-3, GETDATE())