it give a "letting out air" sound and it goes all the way to the floor

Hello,

This could be a problem with your vehicle's brake booster.I would suspect there is air in the lines. These guides can help you fix it.

https://youtu.be/w7gUsj2us0U

and

https://youtu.be/WDxvEQrMkBg

and

https://www.2carpros.com/articles/brake-pedal-goes-to-the-floor

Please run down these guides and report back.

Please go through this guide and get back to us with what you are able to find out.

Thanks,
Alex
2CarPros