I have backed up my chat history but I don't see a restore page when signing up for KakaoTalk.
You may not see the Restore page if:
(1) You have not backed up your data in advance;
(2) You have unregistered from KakaoTalk or removed your Kakao account;
(3) You have reinstalled KakaoTalk and verified your phone number but have not logged in with your previous Kakao account and thus you have been considered signing up as a new user.
Please note that in the cases listed above, restoring your previous chat data is not available.