craft.fields.getFieldByHandle() has been deprecated

I’m querying a dropdown field to loop through all of the options and followed best practice (so I thought) in the twig template. Does anyone know how to update for the deprecation below?

Deprecation message:

craft.fields.getFieldByHandle() has been deprecated. Use craft.app.fields.getFieldByHandle() instead.

Code line:
{% set siteOptions = craft.fields.getFieldbyHandle('siteSelector').settings.options %}