When I use Postgres.app, it uses version 9.6.
I have version 10.5 installed as well (via Homebrew) on my computer and want to use that instead.
When clicking on the + sign in the sidebar to "Create new server" I only get a dropdown with versions 9.5, 9.6 and 10.
How do I instruct Postgress.app to use 10.5?
On
You would have to install the corresponding version of the app which supports your required version from this link, in your case last option might work. https://postgresapp.com/downloads.html
The version you installed with brew is in a different $PATH. It is an independent installation from the one you installed with Postgres.app