archive means a collection of historical documents or records.
its sooo simple.
just open your whatsapp and go to options menu like this
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now select option "settings" like this
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now select option "chats" like this
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now select option "chat history" like this
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now select option "ARCHIVE ALL CHATS" like this
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now select "OK" to archive all chats like this
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now if you want to unarchive all chats.
then select "unarchive all chats" like this
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now click OK to unarchive all chats.
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thankyou :-)