date variable manipulation

I'm working on DB2 stored procedure, which will be called by the Korn Shell (.ksh). My DB2 version is 11.5 and it is running on AIX. I was stuck in TIMESTAMP to DATE conversion. Below is my requirement. If s_day < day(s_date) then start_date = YYYY-MM from s_date + 1 day from s_day end if Note here s_date is DATE variable, s_day is CHAR variable and start_date is DATE variable. So I tried, the following code, but got an error. IF s_day < DAY(s_date) THEN SET start_date = DATE (DATE(s_date,'YYYY-MM') || s_day + 1); END IF Sample values s_day =03 s_date= 15/05/2020 expected output start_date is 2020-05-04 Can anyone help me to achieve expected output?