Undo “report text message as junk”

Hi fmasoli,

Unfortunately, it is not possible to undo reporting a text message as junk. The article also mentions that: Block phone numbers, contacts, and emails on your iPhone, iPad, or iPod touch - Apple Support

Messages will forward the sender's information and the message to Apple, as well as delete the message from your device. You can't undo deleting a message.

Reporting junk doesn't block the sender from being able to send another message. If you don't want to receive these messages, you need to block the contact.