Merchant's tab upgrade

So I wanna convert one of the premium tabs I have on my account from PoE 2 website but I saw there's no way to know which tab is the empty one, I have emptied one of the premium tabs in the game and the order of my tabs have been altered I mean like the default name number before changing them to personal liking, so that's the problem, I've played for a week this new league and bunch of stuff I've organized in the other tabs I have, I left just 1 premium tab there which I intended to upgrade to merchant's tab but there's no way to know or to pick that one from the website as it only shows the date of the tab's purchase and I have no idea which one is the one that is the empty one I've set, I'm afraid if I upgrade randomly pick one of the tab it would pick the one currently holding my important stuff in game and the stuff in that tab will be gone, so if there's a way that I'm not aware of I'd appreciate it to know how