/*
 * replace these values
 * <wp table prefix>
 * <search value>
 * <replace value>
 */

UPDATE `<wp table prefix>_postmeta`
LEFT JOIN <wp table prefix>_posts ON <wp table prefix>_postmeta.post_id = <wp table prefix>_posts.ID
SET
    /* we use meta_value cause that is where the acf saves its data */
	<wp table prefix>_postmeta.meta_value = REPLACE(<wp table prefix>_postmeta.meta_value, "<search value>", "<replace value>")
WHERE
    /*
     * be careful with the matching % is a wildcard, and in this case it would match
     * anything before the search value and anything after
     * make sure that is what you want
     */
	<wp table prefix>_postmeta.meta_value LIKE "%<search value>%"