Once you set up one or more connections, you’ll have the option to manage your connections via Settings -> Manage Exchange Connections.
You can disconnect an Exchange Account Connection by tapping on the connection and then selecting 'Delete connection'.
Be aware that all trades & data imported by this connection will be removed as well! If you previously chose to ‘Remove existing ... transactions’ during the set up process, this old data will be put back.
This way Exchange Account Connections are reversible (as a whole) if you are not happy.