That's not a format: it's a VBA function that will product a new value.
You put it In the BeforeUpdate of the text box on your form, or you can use
it in an UPDATE query to change what's stored in your table.
I think Doug miss-spoke.
If you are doing this on a form, to change just entered data, it
belongs in the control's AfterUpdate event.
Display the control's property sheet.
Click on the Events tab.
On the AfterUpdate line, write:
[Event Procedure]
Then click on the button with the 3 dots that will appear on that
line.
When the code window opens, the cursor will be flashing between two
already existing lines of code.
Between those 2 lines, write:
[MyText] = StrConv([MyText], 3)
Exit the code window and save the changes.
Change [MyText] to whatever the actual name of the control is.
Note... If you use the function in an update query, you must use
strConv([MyText],3).
In a VBA code window, you can use either vbProperCase or it's value,
3.