Greetings EngliA01,
Sounds like you’re asking two different questions here and we’ll attempt to answer them both.
First, restoring your calendar from an archive. This would only be an option if the calendar that was deleted was syncing with iCloud. It looks like you found the article with the steps on how to do that - If you accidentally deleted your calendars, bookmarks, or contacts from iCloud Are you attempting to access the restore options on a computer’s web browser? If so, and there is no option for restore then chances are there may not be data to restore.
Second, if you’re looking to reinstall the Calendar app itself you can do that from the App Store by searching for Calendar. Here’s a link: Calendar on the App Store. If the data is still stored in iCloud and it’s just the app itself that got deleted then reinstalling the app should bring it all back. Delete built-in Apple apps from the Home Screen on your iOS 14 or later or iPadOS device or Apple Watch
Restore a built-in app that you deleted
1. On your iOS or iPadOS device, go to the App Store.
2. Search for the app. Make sure that you use the exact name of the app.
3. Tap the Redownload button.
4. Wait for the app to restore, then open it from your Home Screen.
If you have an Apple Watch, restoring an app to your iPhone also restores that app to your Apple Watch.
Thanks.