Derive a string form fields of subform and main form

[Np02]

Hi, I have a field called VID (visit ID) in the frm_Main Main Form). There is a subform called "Member ID Subform" placed inside the frm_Main. There is a field called DOV (Date of Visit) defaulted to enter Date()(Today's date) in the frm_Main. I want to make the VID field in frm_Main able to automatically derived in combination of the field of Member ID in Member ID Subform, a Hyphen "-", and the date in format of yymmdd from frm_Main. How do I do it?

This is the example: Member ID in Member ID subform is "JA123" and Date in the DOV field of frm_Main is 02/17/03. The VID will be pop out as "JA123-030217"

Appreciate anybody can help.