Nobody can reply to your question. It lacks any kind of useful information which would help us understand what exactly you are doing and what error messages you are receiving. Without at least these two clues nobody can help you.
What exactly are you doing and what is the exact error message you are receiving? Screenshots would be appreciated but not mandatory.
Also note that Joomla! and its extensions can still not work reliably on PHP 7.2. Moreover, PHP 7.2 is not stable yet, i.e. it's not guaranteed to not crash in unexpected ways. Please use PHP 7.0 or 7.1 at least until June 2018 or whenever Joomla! 3.9 is released.
Nicholas K. Dionysopoulos
Lead Developer and Director
🇬🇷Greek: native 🇬🇧English: excellent 🇫🇷French: basic • 🕐 My time zone is Europe / Athens
Please keep in mind my timezone and cultural differences when reading my replies. Thank you!