how can i delete my mail in icloud

See the article Delete email in Mail on iCloud.com - Apple Support

Delete messages

1. In Mail on iCloud.com, select the message or messages you want to delete.
2. Tip: To select all messages in a folder, press Command-A on a Mac (or Control-A on a Windows computer).
3. Do any of the following:

• • If you selected one message: Click  at the top right.
  • If you selected multiple messages: Click Delete.

If you see  instead of , you have “Show Archive icon in the toolbar” selected in Mail Preferences. See Archive email in Mail on iCloud.com. To delete a message or messages, do one of the following:

• If you selected one message: Click  at the top right, then click Trash Message.
• If you selected multiple messages: Click Move, click Trash, then click Move.