According to Samsung Notice, Galaxy J7 Duo should get update in month of July. If you didn't get it till now. Try checking Software Upadte on various platforms. Or contact Samsung.
According to https://www.samsung.com/in/support/in-mobile-phone-part-cost/The price to repair the display is 2,527/-. Go through this official website.
Go to Secure Folder's Settings. Open Lock Type, from there choose dedicated fingerprint option and select one of pre registered fingerprint or add a new one.