The Hubspot plugin for Salesforce allows to add an Iframe on your SalesForce detail screen (contact, lead, account and deal) and shows the activities that are known on HubSpot.
For a fresh installation of the SalesForce integration in HubSpot, you are automatically taken to the installation link of the SalesForce addon.
If you already have installed the SF integration, but for some reason you need to change the connection to a different SF-account where the plugin is not yet added, you can find the plugin via this link:
https://login.salesforce.com/packaging/installPackage.apexp?p0=04t0B00000063ZS
Please note however that is for the 3.0 version. If the customer is looking for a different version or has any troubles with that link don't hesitate to let me know!