BEFORE
AFTER
This super tip has always been on the installation page of Arch Linux in Phase 5 and also here.
It merits some more attention because it gives you the opportunity to start again
as if the nvme, ssd or harddisk were just coming out of the shop.
All data structures will be deleted including gpt and mbr!
Remember these two commands that can help you when you want to remove everything.
wipefs -a /dev/sda
or
sgdisk -Z /dev/sda
Find out what your devices are called with
lsblk
and adjust your commands accordingly.
If you get stuck for a reason, see if gparted can help you.