Schwa is the most common vowel in English and has no letter of its own. Unstressed syllables shrink to a quick, neutral uh, which is why chocolate has two clear syllables and banana sounds like buh-NA-nuh.
Say the stressed syllable fully, then let the others go weak: jaw half open, lips relaxed, very short. Saying every vowel at full length is what makes speech sound foreign.
14% of 53,365 scored /ə/ sounds in the SayWhat app were scored red, from at least 5,537 learners.