Review of how to form stressed "er": Make a circle with your lips and feel your lower jaw move slightly forward. The sides of your tongue should press against your upper side teeth toward the back of your mouth. Raise the tip of your tongue up toward the roof of your mouth, making sure it does not touch anything. The stressed vowel "er" occurs in an unstressed syllable. The vowel "er" and consonant "r" are formed the same way, with one exception: the tongue is more relaxed for vowel "er" and more tense for consonant "r".
Learn how to pronounce the stressed vowel r sound.