If you want to disconnect your external drive from Bitrix24, you need to remove Bitrix24 Connector in the external drive's settings.
Go to www.google.com and open your account.
On My account page, go to Google Account Settings > Connected apps and Sites > Apps connected to your account > Manage apps > Bitrix24 Connector - remove the connection.
Go to www.dropbox.com and open your account settings:
On your Dropbox settings page, open the Apps section.
Find Bitrix24 Connector and remove it.
Go to www.box.com and open your account settings. In the Security section, find Bitrix24 Connector and remove it.
Office 365 / OneDrive
Log in to your Microsoft account and open the Privacy section. Scroll down and select View apps access details.
Find Bitrix24 Connector and click Edit > Remove these permissions.