If you want to email directly the President of IKEA US, his name is Mike Ward. Please follow the following email exactly but try both because it may be under Michael or Mike: Mike.firstname.lastname@example.org Michael.email@example.com
Hope this helps for the unhappy customers.
I know many companies don't like to have their experiences pass the stores to the main headquarters or try to not get to the US level within their organization. Here's your opportunity.
The format is the same for any person within IKEA as long as you have their first and last name. First name first then a dot then their last name and then @ikea.com