Start UI horizontal?

Hello everyone, what do I have to do to start the UI Horizontal Which file needs to be customized and with what content. /flash/config.txt or /usr/share/bootloader/config.txt or /flash/distroconfig.txt or /usr/share/bootloader/distroconfig.txt

I cannot edit the config.txt. even with root right

Must the following value be included? lcd_rotate=2 or anything else thanks for a short help

The /flash partition is mounted read-only, you need a PC to edit the file. lcd_rotate=2 should work yes!