'windows' disc keeps popping up on startup disk manager

i want to get opencore on my late 2013 mac so i can run all the apps that have stopped recieving support. however when im on the disk selection screen, mine looks nothing like the one shown in https://dortania.github.io/OpenCore-Legacy-Patcher/BOOT.html i believe this is because my pc came pre installed with a windows disk somehow that i CANT get to eject somehow. anyone got a fix? the disk i want to select is downloaded in the same disk that already contains windows so i cant load it up