Hi Team , I am unable add my Debit Card Detail in Payment method .Kindly assist

What happens when you try? Error message(s)?

Log into your account in the App Store/iTunes and you should be able to change/verify it there. Or you can click the blue Edit payment methods in the article below. When signed in and the page loads, you will be on the credit card page. After updating that, click the Go Back button at the lower left and you will be on the address page. If you have a subscription, you need to add the new card, and then promote it to the primary payment method before you can remove the old card.

Apple ID payment information - change.  

See the Apple Support article(s) below. Link to contact Apple Support in the article. 

Apple ID payment information - If your payment method is declined, or you have a billing issue with a previous purchase in the iTunes Store.    

Possible fixes.   Fix ‘Your Payment Method Was Declined’ Error In App Store

                          Payment method declined in iTunes or the App Store.