I was just learning DaVinci Resolve
and accidently clicked Blade Edit Mode
It's now shown as follow. red
How do I deselect it?
So you can just click Arrow button, or press "A". To select blade again, press "B".
Now that you know how to turn the mode on and off, you may want to learn a little more about what it is. The blade tool is very convenient thing to cut video instead of dragging by the end of footage.
I'd strongly recommend considering "Blade + select + delete" editing. It's working tool.
Now there are two ways to use interface in such editors: