If your entries are like "2017:11:20 17:04:01", and you just want to get the valid date out of it in a query, use this calculated field:
Code:
CDate(Replace(Left([Registration Date],InStr([Registration Date]," ")-1),":","/"))
Note that the FORMAT function returns a string, not a date. So you typically wouldn't worry about the formatting of the date in the calculation, you would handle that in the Table or Query Formatting property.
If you had wanted to return a String and not a Date, then you could wrap that whole calculation in the Format function, i.e.
Code:
Format(CDate(Replace(Left([Registration Date],InStr([Registration Date]," ")-1),":","/")),"dd/mm/yyyy")
Just note that in a Make Table query, the first calculation will set up a Date Data Type while the second will set up a Text Data Type.