I need to convert
You shouldn't be performing a text conversion at all.
You should be storing the data as a DATETIME (or whatever the corresponding type is in the database) and then you should be specifying the value in the query using a parameter, not including it in the SQL.
That way you don't need any string conversions in the first place.
Always pass values via parameters unless you have some really, really good reason why you absolutely have to include it in the SQL directly. Using parameters: