You have to install all missing extensions that you saw during readiness check.
If you have direct access to the server, and you're able to install extensions, just execute
sudo apt-get install php5-intl php5-iconv
And you'll have to do the same for other missing extensions.
If you don't have access to it, you'll have to ask your System Admin or Hosting provider to install those extensions for you. That's the only solution.
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