It is recommended in general to use independent plugin to add analytics code rather than adding it via theme

• Can be added via customizer settings.
• This is not a built-in setting for Google Analytics Tracking, but a general provision to add any type of code in header.
• Copy your ‘Tracking Code‘.
• Find it in Google Analytics under the ‘Admin’ panel. Refer google docs for more info.
• Make sure you are copying the ‘Tracking Code‘ and not the Tracking ID or User ID.

  

• Go To : Appearance > Customize > General Settings > Custom Code in Header > Code in Header
• Paste the code in textarea, along with ‘script’ tag