So that the Community can help you better, we need to know exactly which Canon camera model you're using. That, and any other details you'd like to give will help the Community better understand your issue!
If this is a time-sensitive matter, search our knowledge base or contact our US-based technical support team at http://canon.us/SupportCF
Thanks and have a great day!
Even without the information of which camera you are having issues with, the easiest way to fix this issue would be to delete the entry in the wifi settings on the camera (It may say Reset connection, or Forget connection, or something similar) Then just setup the connection like you did the first time.
That being said, it is always a good idea to state the camera you are asking about, and any other relevent information such as iphone version, and OSX version would have been helpful too.