VBA to copy data to new column if date doesn't allready exist.

Hello guys, first post here !

First off I know that there are a lot of similar use cases for my problem but my knowledge is just not good enough to adapt it to my situation .. so here goes ..

I have a workbook in which the user fills in values in Sheet1 (C5:C20) and at the top of Sheet1 (C2) the user fills in the date.

Now I would like a vba code to copy the values that have been entered into Sheet1 (C5:C20) to another sheet (Geschiedenis) like this:

_____A_____B_____C____
1 | date1 | date2 | date3
2 | valu1 | valu1 | valu1
3 | valu2 | valu2 | valu2
4 | valu3 | valu3 | valu3
etc...



and here's the catch.. it has to check for that date (primary key) if there are existing values or not and if there are it should overwrite them.

I hope I'm making sense and any of you can find the time to help a noob out ..
My boss would be super-happy :p