Arch Wiki has a rather decent article about wiping disks: https://wiki.archlinux.org/title/Securely_wipe_disk
Assuming your Pi runs a Linux distro, most of those tools should be already present on your system.
Arch Wiki has a rather decent article about wiping disks: https://wiki.archlinux.org/title/Securely_wipe_disk
Assuming your Pi runs a Linux distro, most of those tools should be already present on your system.