Can't transfer account data?

it didn't work. I have an idea tho, I could possibly try to delete both my FEH apps on my ipad and old iphone but I'm worried that I'll lose my progress, considering I've put over a year's work into this game I'm too much of a bitch to test my luck. I'm also worried that when I linked my data it overwrote my first account's data. I'm not entirely sure if that's even possible also taking into account that I can still play my old account, but I'm grasping for anything at this point.