If the devices are company-owned, the safest approach is to use a Surface Recovery Image or Windows recovery media to perform a full wipe and reinstall of Windows. This does not require access to the previous local administrator account, but any data not backed up will be lost. Reset or recover your Surface explains how to reset or recover a Surface using recovery media.
Be aware that if the devices are still enrolled in Microsoft Entra ID, Intune, or Windows Autopilot, they may reconnect to the organization's management tenant during setup and could require access to the organization's Microsoft 365 administrators.
If the data on the devices is critical, try to assess recovery options before wiping, as a reset will permanently remove local files.