As long as your CD-R disc hasn't been finalized, you can erase it and reuse it the same way you could a standard CD-RW disc. The finalization process is what makes it impossible to reuse a CD-R after its been recorded to, and so long as that hasn't actually happened yet (usually the "finalize" box is checked during burning), you can continue to record data to a disc as often as you'd like.
Insert your CD-R disc in the computer CD burner drive.
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Right-click on the circular CD-R disc icon.
Click "Erase." If the CD-R disc hasn't been finalized, your operating system will erase the contents of the disc, allowing you to use it again. If the disc has been finalized, a message will pop up on screen telling you the command cannot be completed.