There's a few problems there so I'll try and explain without it being too confusing. I went with the variable method because I don't like the angle logic but it looks like you are using angle so maybe it's ok to use this instead (assuming the walk animations are correct for you).
The main problem is those angle conditions for walk animations are running all the time so you won't be able to set an idle animation. They need to be 'sub events' but are currently just listed underneath as separate events which doesn't mean sub events in construct. You need to press S and add them so they are indented under 8 direction is moving event. That was maybe your problem from the start.
So ignore the variable logic I mentioned, when you have fixed it so those angle checks are sub events/indented on the 8 direction is moving logic, all you need to do is copy and paste those events, change 8 direction is moving to inverted, and change your animations to the idle ones.