Cannot figure out how to discard from collection

[Lizlo6]

The rules sate that if you already have 6 cards in your collection, you need to delete one to add a new one. I accidentally did have 6 once, and could not figure out how to delete one. I have also been in matches with other players who have been stuck in this position. Yes, I realize that collecting cards you might later have to discard is a terrible strategy, but since the rules say to do it, I assume there is a mechanism and I am just not seeing it.

Can anyone enlighten me here? Thanks!

[jordijansen]

When you would collect your 7th set, you are automatically promted to discard one of your sets.

[Lizlo6]

When you would collect your 7th set, you are automatically promted to discard one of your sets.

I tried that, and it was not the case. I just was not allowed to add anything.

[jordijansen]

This is the prompt you get when you add your 7th set:
https://snipboard.io/DCTHkF.jpg