I don’t know exactly what stage you’re in now.
Just get rid of debian as petsam said. just format out the debian partition.
If you have to reinstall Manjaro, suggest you do not have a boot partition, unnecessary and more hassles to handle. Get partitions ready for installation and install. That’'s it.
If you run into problems and cannot boot, take a look at the first post of this. I won’t think you will run into any problem. I can’t see why you should, actually.
I would recommend you to listen to petsam for issues like this. He will get you up and running.
Except he’s sleeping now. Not like me who doesn’t need sleep.