Welcome to the world of auto repair. I think the engineers that design the automobiles should have to work on them for one year. They might design them to work on them. Here's a video to explain what needs to be done. You better try to find a way to get to the hoses, because the alternative is something that you won't want to do. Replacing the heater core is real fun, NOT. Few this video. good luck
This is the proper way to flush a cooling system.