“ReceiverHelper” will damage your computer.what is this about and how to quit and close this alert?

A couple possibilities come to mind. They may or may not be malicious.

Please download and run EtreCheck. A download link and instructions are included in Old Toad's User Tip, here:

How to use the Add Text Feature When Posting Large Amounts of Text, i.e. an Etrecheck Report - Apple Community.

Post that report in a reply to this Discussion in accordance with its instructions. It is almost certain to identify the culprit, after which someone can suggest remedial action.