UEFI-installed Debian on a pendrive doesn't want to boot after being removed once

I read here, once, that installing a Debian 9 on a pendrive (well, in my case it's a SDCard adapter) directly would work, and it did. The problem came up, though, after i unplugged the adapter from the computer; when i wanted to boot into linux, all i had to do was to choose the boot device labelled 'UEFI: debian' on the bios setup, but as soon as i removed the adapter, that option disappeared. I don't want to lose the debian installation, I want it working again. I need to get it booting again.