Confusion in Pronouncing Shaddah on "ي" During Prayer

Assalamualaikum. If a person knows that whenever there is shaddha on ي , we have to hold and then let go . If the person watches the videos of pronunciation of surah Fatiha and Tashahhud , before every prayer and thinks that when ي is to be hold , lips must move like tremble like , and when that person prays , gets confused , like he/she knows lips moved but doesn't know if sound was correct , of sometimes the whole face will move , like shake a bit . Sometimes sound will come but he / she does not know if lips moved . And many times , the way it is pronounced is not like how the person in the video pronounced it and watched other videos and it is different , all are holding the ي but the sound is different . What to do in such case