What do i have to do to get the achievements after I added the items to my wardrobe?

you have to wait a bit then visit the achievement's page, one like this: https://subeta.net/achievements.php#/achievement/1399 and click "show required items"

This includes visiting your wardrobe and then waiting then going to the achievement page. I don't think it works without actually viewing your wardrobe.

Thanks, got it

It's very simple:

Go into your wardrobe regularly, especially if you add items, then come out and check the achievement pages. It might take a little while to update, depending on the site that day, and remember that if you take anything out, you have to go past that last number.

It always read the highest one as your progress. Like if you have 2500 items in your wardrobe and you take out 50, you have to reach 2500 again and go past that for it to start counting again.