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' from the "3-dot menu" in the top right.
When you delete you will be asked if you want to KEEP or REMOVE the transactions imported by that connection.
The transactions previously imported by that connection will remain as is and the connection will be deleted i.e. it will not import future transactions.
It will remove ALL transactions added by the connection. This action is irreversible! If "Remove existing transactions" was enabled when adding that connection, this will also restore the manual transactions that it had removed. This way adding Exchange Account Connections are reversible (as a whole) if you are not happy with the import overwrite.