You can to use tags + conditions to stop the messages from sending.

When they finished the conversation, tag them with a tag 'Finished Conversation' or something similar.

And at the beginning of the flow, add a condition that only sends the message if the tag ISN'T 'Finished Conversation'

Still didn’t get it can you explain with some more details really appericated !! or any tutorial i can follow 

Something like this…

With this automation the person will see the message only once, no matter how many times the flow triggers.