If you want to disconnect your external drive from Bitrix24, you need to open external drive's settings & remove Bitrix24 Connector. Here is how:
Google Drive
Go to www.google.com and open your account.
At "My account" page go to Google Account Settings > Connected apps and Sites > Apps connected to your account > Manage apps > Bitrix24 Connector - remove the connection.
Dropbox
Go to www.dropbox.com and open your account settings:
At your Dropbox settings page, open Security section.
In the Apps linked section find Bitrix24 Connector and remove it.
Box.com
Go to www.box.com and open your account settings. In the Security section, find Bitrix24 Connector and remove it.
Yandex Disk
Go to disk.yandex.com and open your account passport.
At Yandex Passport page, click Access Management.
In Apps access section, find Bitrix24 Connector and remove it.