How to re-invite member to conversation?

[jaeitee]

Hi, we have a "Team" conversation in our messenger and one of the team members has mistakenly left the conversation.  His name is now greyed out at the top and I can not work out how to re-invite him in to the conversation opposed to having to start a new conversation and re-invite everyone.  

There's some valuable information in that conversation, hence the desire to invite him back in opposed to create a new conversation.

Any pointers? Or can it be done in the database?