In order to enable the Salesforce data connector and create a Salesforce connector, you must meet the following requirements:
Have an owner or admin role in the respective Mixpanel project.
Have a Salesforce account with API access. This can be achieved by either having “API enabled” checked off in your user profile by your Salesforce administrator, as shown in the image below, or having this API permission as part of one of the organizations permission sets. Additional details on how to enable "API enabled" can be found here.
If you have both these permissions you'll be able to successfully connect Salesforce to your Mixpanel project by going to the “Data Connector” tab in “Project Settings”.