If you have shared a report as an online link and want to remove access, there's a couple of ways you can do it.
If you no longer need to keep the report active you can archive it from your account. Click on the 3 dots below the report and you can Archive it. The report will go into your Archive folder, where you can restore it any time in future when needed.
If you want to stop access to the share link but still keep the report active in your workspace, head to the Reports tab and open up the menu (click the 3 dots). Then select 'Copy' followed by 'Copy with Coverage' in order to create an exact copy of the report in your account.
You can now archive the old report and share link. Select the 3 dots again and this time select 'Archive'.
You'll now have an exact copy of your report but with a new URL.