About select the file on the Timeline Panel

[longinus1]

I used to select one single file with its audio by simply left-click it. However, I may misclick some button today and the selection tool turn to select everything on the timeline even they are cut by razor tool. I have to select with alt+left-click to single select now. I wonder how I can go back to the older setting.

[R Neil Haugen]

Make sure you're using the V tool, the basic selection tool. Is that arrow for it blue on the tools panel?

Neil

[longinus1]

Yes, I'm using the V tool and it just selects everything on the track.

[Peru Bob]

Try resetting the preferences:
https://community.adobe.com/t5/premiere-pro/faq-how-to-reset-trash-preferences-in-premiere-pro/td-p/...

If that doesn't work, try resetting the Workspaces:
Reset a workspace
Reset the current workspace to return to its original, saved layout of panels.
1. Do one of the following:
• Click the Workspace menu icon and select Reset to Saved Layout.
• Choose Window > Workspace > Reset to Saved Layout.
from here:
https://helpx.adobe.com/premiere-pro/using/workspaces.html