Control C

Now that you know how to Copy and Undo, try using Undo again.

You did not describe the app you were using, but most Mac apps support many levels or depths of "undo". So try opening that document again, and use ⌘ z.

Subsequent ⌘ z actions will keep "undoing" to the extent the "undo" buffer is retained. Perhaps your missing text will reappear.

If that doesn't work, you might also be interested to know most Mac apps support versions. In Pages (for example) you would use File > Revert To... > Browse All Versions...

View and restore past versions of documents on Mac - Apple Support

Excerpt:

Many apps automatically save versions of documents as you work on them. At any time, you can browse through document versions and go back to an older version. You can also explicitly save a version.

A version is saved automatically every hour, or more frequently when you’re making many changes. A version is also saved when you open, save, duplicate, lock, rename, or revert a document.

Hi,

I think you can't salvage your text.

Command+c is the copying texts.

I am used to using a windows platform.

Are you new to Mac? - Apple Support

and Mac tips for Windows switchers - Apple Support

Command is your new Control.