Debian install blocks booting of flash drive

Today I bought a new Samsung laptop and decided to install Debian 10.2 into it. I've flashed the image onto flash drive, disabled secure boot in BIOS and booted the installation. The installation was performed incorrectly (because of fault firmware detection that couldn't connect to the internet but the installation requires internet to complete) which resulted in incomplete installation. The laptop then rebooted and booted into classic option boot menu of Linux and started Debian with just a command line which after login does nothing. No GUI no normal login no nothing. So I decided to fix the issue with USB to Ethernet adapted for the next installation but now I cannot boot the flash drive correctly because Debian always overwrites the flash boot even if the flash drive is selected as the first two options and for the last I've chosen "Disabled" to prevent Debian from booting up but that had no effect and Debian still booted up first. So now I cannot boot the flash drive and I have a broken install of Debian on my laptop. What do I need to do to fix this issue? Thanks to anyone.