Install a Previous Version of Salesforce CLI
By default, the latest version of the salesforcedx plug-in is installed when you install or update Salesforce CLI. If you need to install previous versions of Salesforce CLI and the salesforcedx plug-in, make sure that your sfdx-cli version and your salesforcedx version are compatible. Salesforce CLI v7 is required for salesforcedx plug-in version 45.8.0 or later. Salesforce CLI v6 is required for salesforcedx plug-in version 45.5.0 or earlier.