as per the requirement,
I have to convert user texts into DB date format
Required format: YYYY/MM/DD
expected date inputs:
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Is 02/12/2022 February 12, or December 2? You literally do not have any way to tell either Appian or the database which it is unless you give up one of the expected input formats or require the user to configure/input which format they're using.
Other than that, try todate() and see what comes out. It may work for most cases, and some you may just need some minor adjustment. You could build a simple a!match() that replaces month text with a number, and then pass those to todate(), if you even need to.