An employee's scheduling who has not yet started their contrat is a little bit different because the Scheduling part, available on the employee's profile, only appears on the first day of the contract.
To prepare the schedules of an employee before the contract start date, go to their profile:
Click on the future contract
Go to the tab "Schedule"
Select the locations where you want to schedule your employee
💡 Good to know :
If the employee had a previous contract, and you unmarked the option “Display on schedule”, the employee will not appear on the schedules ! You need to see them to schedule their future shifts, you can temporarily move forward the start date to activate the option before indicating the real start date again !