Hi Arovin,
Welcome to our community! 
I’ve watched your video multiple times but, unfortunately, I do not understand what you mean. To me, the movement of the bird looks fine. Could you please point me to the second in the video where the problem starts?
If you use the new input system, maybe Nargleflex’ answer will help:
https://answers.unity.com/questions/1773182/smooth-input-in-new-input-system.html
See also:
- Forum User Guides : How to mark a topic as solved