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 & 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 & open your account settings:
At your Dropbox settings page click "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 & 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 (or Bitrix24) and remove it: