I'm new to the site, I started adding my EDH decks to my profile but instead of first adding the cards to my inventory, I just made deck lists with the cards I own. The problem is that the cards from these decks aren't showing up in my inventory, I tried exporting to a CSV file then importing back in my inventory but It keeps telling me 'header' is wrong in the CSV file. Any suggestions besides re-entering all 5 EDH decks?

The CSV export for a deck is different than the one for the inventory. You should be able to get it to work though by opening it in Excel or some spreadsheet processor, removing the Sideboard column, and adding a second column after Count called "Tradelist Count"