If your devices is bought without Autopilot registration you need to register it first by using Get-WIndowsAUtoPilotInfo.ps1.
Normally to achieve this you would boot into Windows and run the script and afterwards you need to reset the windows device to factory default.
This would take a certain amount of time.
A much quicker way is to boot the device till the first OOBE screen, the press Shift+F10 to open command and powershell, install and execute the script. Import the device in AAD and reboot your device.
Boot Device into OOBE
Press SHIFT + F10
This will open the command prompt
Type powershell and press enter to start powershell
Type Install-Script -Name Get-WindowsAutoPilotInfo
If installation fails you could manual install the script by downloading the script from https://www.powershellgallery.com/packages/Get-WindowsAutoPilotInfo/1.3
Edit your execution policy and run this command.
Get-WindowsAutopilotInfo.ps1 -OutputFile AutopilotHWID.csv
Import the csv into Azure AD Autopilot devices.
Wait a few moments and reboot your device. It will now autopilot.