While I'm inside the car I can't open the door. ..how I can fix it ?

The handle has somehow become disconnected from the mechanism that opens your door. It's probably a simple problem. The line has broken somewhere. Or the line came loose and you just need to reconnect it. Either way, you'll probably have to take the inside of the door off to see why it's not connected. I had to take my inside door off recently to repair a door check. To be able to do that, I watched a YouTube video for my car make. That enabled me to be able to take the door off and make the repair.