How do I restore missing events on iPhone Calendar app?

Can someone help me - Yesterday I noticed my red tag - from my outlook was not adding to my calendars, which is used regularly. It kept disappearing straight way. After updating dating phone and going through check list on the internet. Nothing was still happening. I then deleted the tag and now I can get it back. I then went to my icloud to restore an older version and its still not back. I have lost a lot of old and new events. How can I get back my original setting and be able to continue to use this certain tag.