Your visitor can contact you via the SwiftReader at your main entry. The visitor should click "I'm a Visitor" > "Call Tenant" (could be Call Resident, just depends on how your Admin has it setup on the backend) > search or scroll to your name and click "Call".
At that point you will receive the intercom call via the Swiftlane app as shown below. If and when you want to unlock the door you can press "Unlock" button to unlock the door for your visitor.
Please be sure that your Notifications are turned on to receive these calls. How to do this you can view this Help Article: I am not getting notifications when an Intercom Call is coming in?