SD Card Copier software writes an image of your SD card to a USB device - perhaps a USB-SD adapter, or a USB storage device?
NOTE: In general, more details make for better questions.
And so I will assume the following:
- You have a working backup on a device that can be plugged into a USB port
- Your RPi remains operational - you can read the USB device with the backup
- You know how to open a terminal window & type commands into it
If this is your situation, you will only need to
mount your USB device - after it is mounted, you can rummage through it as you wish, and find your text file.
- Plug the USB device containing the backup into a USB port on your RPi
- open a terminal & run the command:
- verify that the USB device appears in the output - it should have two partitions:
mount the USB device or partition; ref
man mount or read this
- find your text file, and copy it to your active SD card
Any follow-up questions should be made by editing your question, and include the output of
lsblk --fs. This concludes "the answer"; I've added some unsolicited advice in the sequel that may help you in the future.
SD Card Copier - there are better backup solutions. My favorite is