How to add text to the new thread button?

This is good example how to add text to the + button:

Just add this CSS:

.bp-messages-wrap .chat-header .new-message {
white-space: nowrap;
width: auto;
padding-left: 15px;
}

.bp-messages-wrap .chat-header .new-message:after{
content: 'New Message';
margin-left: 5px;
}