I think I deleted all my data on my current calendar??How can I get the last backup from iCloud?

Try recovering your calendars at iCloud.com. Click account settings. Then scroll to the bottom and select "restore calendars" under Advanced. You'll need to use an iPad or computer to access the link.

Depending on the account that your calendar is attached to, you may be able to restore items from trash.

You can restore your device too if it hasn't synched with iCloud since the items were deleted (check your status at Settings > {your name} > iCloud > iCloud backup (https://support.apple.com/en-us/HT204184)