It's the green app with a white phone and chat bubble icon. If this is your first time opening WhatsApp, you'll need to set up WhatsApp. It's in the bottom-right corner of the screen. If WhatsApp opens to a conversation, first tap the back button in the top-left corner of the screen. It's near the top of the page. This option is at the top of the "Account" page. This green switch is at the bottom of the screen; sliding it left will disable read receipts in non-group conversations, which will in turn prevent the blue "Message Seen" ticks from appearing in your chats. If the switch is white, read receipts are already disabled.
व्हाट्सएप (WhatsApp) ओपन करें: Settings पर टैप करें: Account पर टैप करें: Privacy पर टैप करें: Read Receipts को "Off" (बाएं) पोजीशन की तरफ स्लाइड (slide) करें: