EU Declaration of conformity kits

I have been asked for an EU declaration of conformity, I created a bundle of items some I had made myself and dont need a declaration and I added a pack of balloons to the kit from another manufacturer. I think this is what is triggering the declaration request. Do I just upload the declaration from the balloon manufacturer or do I have to create the declaration as the kit belongs to my brand? Any help in this mine field would be really appreciated.

Thanks