returns the date-time serial number, from a date given as text.
Syntax:
DATEVALUE(datetext)
datetext is a date, expressed as text. DATEVALUE returns the date-time serial number, which may be formatted to read as a date.
Example:
DATEVALUE("2021-12-15")
returns 44545, the date-time serial number for 15 Dec 2021 (assuming the default date-time starting date)