Question: forgotten itune backup password
I have purchased iphone 7 plus recently. when I take a backup of my old iphone 6s in itune and transfer it on my 7 plus itune ask me to enter backup password. after so many attempts I can't transfer my data to 7 plus through itune then after googling somebody ask me to transfer all data through icloud. which I did but my question is this how can I get my backup password again and when I want to restore my old 6s phone my phone want a restriction password what was that. Please help.
iPhone 7 Plus, iOS 11.2.6