It depends on what version of ACF you’re using. 4 (from the WP repo) or 5 (Pro version)
In both cases you’re going to use get_terms() https://developer.wordpress.org/reference/functions/get_terms/
In the most recent ACF 5 you can use use a meta query.
With ACF 4 you will need to get all the terms and loop through them to find the one with the right value, this is the same for any version of ACF < 5.5.0
