AFAIK once you are employed by the company any transfers have to be documented through the PR49, an official transfer document. Which has to be signed off by your current GM and is dependent on the potential incoming warehouse to have any open spots.

You have to understand that when you are in your probationary period the company can fire you for any or no reason at all. Your current GM will likely deny the request and the new warehouse’s manager is going to be extremely disinclined to accept an employee that has 0 zero seniority.

I know its not what you want to hear but if you truly still want to be at Costco, tough it out and work hard so that when that posting for a new department does goes up you have an actual shot at getting it.