Hi, recently downloaded anki on my desktop (primarily use it on iphone and macbook), and set everything up, but as of recent, there is two different anking-mcat categories. I’ve attached a screenshot. I’d appreciate help in combining them or figuring out what the issue could be.
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Hello,
I’d be happy to help. 
First, let’s make sure that you have the correct amount of cards and no duplicates.
Can you go to the Browse screen, click on this tag, and let me know how many cards are listed as being present?
6278
Cool.
So the good news is that all of the cards that should be present are, indeed, present.
The bad news is that they’re seemingly not in the organizational pattern that you want. Easy enough to fix, though.
There are a couple of ways to do it, but the fundamental move here will be going into the Browse screen and moving the cards around. This can be done by selecting the cards you want to move, right-clicking, and selecting ‘change deck’:
There’s not one way to go about this. You can move from one ‘Chemistry’ deck to another, or move by tags, or some combination of the two. In a pinch, should only take about 1-2 minutes and you should be right as rain.
Once you’ve moved cards out of whichever decks they will then be empty. At this point you can just delete the empty decks and be on your way.
Let me know if this makes sense, and/or if there is anything else I can help with.