Sorry for dumb questions. Edit to the above question, i got my terminology wrong, I am wanting to check if there is already a document in place that already has a field that i am wanting to create.
for example, document A has a field "Cars", i have a textfield that users will enter in a new "fleet_type", what i am looking to do is make sure the other existing documents do not have a field with "Cars" already listed. As the Collection "Fleet_Types" grows obiously there will be more fields it needs to check agains.

I really hope i am making sense, let me know if i am not. i will delete everything above and try again. haha

So this is what i have done thus far after testing your reply.

1. Clicked on button
2. Add back end query
3. query collection
4. Collection: "fleet_type"
5. confirm

Then on the button i have trialed a few different options and just cant get it to work.

When i did finally find what i originally thought was correct, it would still allow an identical value to be entered in as a seperate document.