Temporary iphone 7 asks for old password

So i have used and iphone 12 which is now given to apple for a warranty change. Temporary phone was given to me which is iphone 7. Now trying to set up the temporary phone it asks for 6 digit passcode which was used on my old iphone 6s which i used before iphone 12. I do not remember the old passcode as on the iphone 12 i've used 4 digit code. What to do?