The Nextcloud desktop client does not provide a way to change the local sync directory. However, it can be done, though it is a bit unorthodox. Specifically, you have to:

1. Remove the existing connection which syncs to the wrong directory
2. Add a new connection which syncs to the desired directory

To do so, in the client UI, which you can see above, click the “Account” drop-down menu and then click “Remove”. This will display a “Confirm Account Removal” dialog window.

3. If you’re sure, click “Remove connection”.

4. Then, click the Account drop-down menu again, and this time click “Add new”.

This opens the Nextcloud Connection Wizard, which you can see above, but with an extra option. This option provides the ability to either: keep the existing data (synced by the previous connection) or to start a clean sync (erasing the existing data).