Since this is a Surface Pro it should have Windows 10 Pro which has group policy available. If you see no mic icon, you most likely have Cortana disabled.
Check the following
- Press [Windows key + r]
- Type gpedit.msc
- Expand 'Computer Configuration' > 'Administrative Templates' > 'Windows Components' > Search
- Locate the setting 'Allow Cortana' and set it to either 'Not configured or Enabled'
- Reboot and Cortana should be on
You may also need to go into privacy settings and enable applications to use the microphone if you disabled that too.