i have an FE Heroes account on my phone with a lot of stuff on it. i don't want to lose that data, so i want to link it to my Nintendo account. however, i already have another, newer save data linked to it, one with the starter units and not much else. if i link my other account when i have the new one already linked, will it delete the good one and bring up the new one's save data?
Usually, when doing this in other mobile games, the moment you link your account to the game your current game savefile will be lost and be replaced by the savefile that is saved on the Nintendo Account.
I don't know for FE Heroes in particular, but I know thats what happens with other big Mobile games that give you the option to 'save to the cloud'