delete/ erase internal SSD MacBook 12"(2017)
Looking for advice on erasing my internal drive to free up ca30GB on two inactive volumes. I am on Mojave but had Big Sur on another (or 2?) APFS volume that I deleted but it looks like I did something wrong. I did not deleted the Big Sur volume from recovery mode but directly from disk utility. Now there are 2 inactive/greyed out volumes that I can't delete and that take up almost 30GB. I tried to delete them in terminal but they were deleted and added again.
I have a bootable Sandisk SSD 250GB usb (with recovery and Preboot partitions) from another Mac with Mojave 10.14.6
Do I have to boot from the external Sandisk, before I can erase/delete my APPLE SSD AP0256J Media (or just the container 'disk1')? Or can I erase/delete my APPLE SSD AP0256J Media from disk utility in recovery mode?
How do I then reinstall the OS? Can I still reboot in recovery mode (command-R) after the ssd was deleted/erased because the recovery and reboot volumes also get deleted/erased???
I do have a Mojave installer usb stick.
Or do I have to reboot in internet recovery mode (command -option-R)?
Thanks
MacBook, macOS 10.14