Open WhatsApp: Launch the WhatsApp application on your device.

Open Contact's Chat: Navigate to the chat of the contact for whom you want to customize the ringtone. 

Access Contact Info: Tap on the contact's name at the top of the chat to access their profile. 

Go to Notifications: Look for the "Notifications" or "Wallpaper & Sound" option within the contact's profile. 

Choose Notification Tone: Select either the "Message notification" or "Call notification" option, depending on which you want to customize. 

Select Ringtone: Choose your desired ringtone from the available options. 

Save Changes: Save the changes to apply the custom ringtone.