Welcome to the Candy Crush Saga Community
Do you have a question or need help with your game? Ask the Community.
Check that your device is supported:
http://candycrushsaga.com/help/en
If you scroll down you can see the iOS requirements. Maybe it's not supported anymore?
If it's fine then maybe the steps here will help you:
https://care.king.com/en/candy-crush-saga/loading-crashing-issues-ios