There are a couple of ways to help your users ensure that their scheduler link appears in their emails, depending on if you always want them to include their scheduler link, or if you want to include them to include their scheduler link in specific emails.
Option 1 (using a custom CRM field, merge fields, and templates): Your organization can create a custom field in Salesforce for the scheduler link, and then insert that merge field into the Template in your Master Flows. This guide contains the recommended setup steps for that custom field in Salesforce.
Option 2 (using email signatures): Have reps include their scheduler link in their email signature, ensuring it appears consistently whenever they send emails.