Hello @AJAY15 - please clarify what it is you are trying to open. Are you trying to look at the similarity report by clicking a button within Canvas or within the turnitin.com website? Or perhaps you are attempting to download the similarity report into a pdf file? Additional details would be very useful and I agree with James about reaching out to support.
Also, the reports may take several minutes to process.
Lastly, when something isn't working as we expect, I always start with the basics: is the web browser up to date? Do you have cookies enabled? Have you tried clearing the cookies and cache?