By default, if your prospect is not in Salesforce or HubSpot CRM or not recognized in the link, they will see a form at the end of the booking link asking them their name, email, and phone number based on the Default Form.
If you want to change this, as an Admin, navigate to Forms within a workspace and Add New Form
Create your fields and point them to the proper Lead and/or Contact fields in your CRM Instance
Once you create a form, tie it to the relevant Meeting Type(s) under "Guest Form" settings by replacing the default.