I think what you're asking (although I'm not sure) is how to have the selections made via checkbox tool by a user in App#1, populate a drop down tool in App#2. If that's correct, you'll have to make use of chained app functionality. App#1 will need to end up in an output that will be the values for the drop town in App#2. You chain the apps together, but publish App#1 making sure you don't mark the output to be used in the dropdown as an asset.
Here's another Community posts where I explain it with an example in the comments:
https://community.alteryx.com/t5/Alteryx-Server-Discussions/Chained-apps-Use-an-output-xydb-of-one-a...
If I'm not understanding your question and this is not what you are looking for, then you'll have to provide a lot more detail including screenshots and configurations of exactly what you did, and how you want it to work.
