How to securely delete a file after it was insecurely deleted (in linux)

How can I securely delete/shred a file after I accidentally deleted the file insecurely?

Let’s say I have Debian Linux installed on a laptop with a 1000T spinning hard disk (so putting aside wear leveling uncertainty and sfill).

I stored some super-sensitive data to secret.txt. For some reason, I decided I wanted to delete this file, but I accidentally executed rm secret.txt.

Using testdisk, I can see the newly unlinked file. I can restore the deleted file’s contents using testdisk, but–afaik–that would just create a new copy of the file (so doing a restore -> shred may not securely wipe the original file’s contents from the disk, and it may actually make the issue worse)

How can I actually shred/srm the blocks containing the original file contents of secret.txt following the accidental execution of rm secret.txt?