Iterate through row and then msgbox if value in column exceeds a set number

Hey guys,

I am trying to solve following issue:
I'd like to iterate through the first row of my table and find a certain string, let's say "w1". I do this to keep the table dynamic for changes.
If w1 was found, the code should go down that column and put out a message box when the value is bigger than 500. Ideally it does that immediately when I type in a number that's bigger than that.
I have tried writing following Code, which doesn't work:

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Can somebody please help me?
Thanks a lot in advance!

Hey AlphaFrog,
this worked perfectly!!
Thanks a lot