Select a TDD champion, the person or people who most support the practice within the team. Have them set up the framework and create the initial approach.

Choose one User Story to implement TDD on. Once the User Story is done, have the champion/champions workshop their findings back to the team and teach them how they can implement TDD as well.

The team should then select the next User Story they'd like to TDD and then pick a team member to pair program (see the next section) the solution with the TDD champion.

Alternatively, if the TDD champion is already a confident TDDer, they could introduce the whole team to the Test-Driven Development approach using workshops, or pair or mob programming. 

Whichever approach you take, you should work in that configuration as a team until the User Story is "done," that is, delivered into the hands of your customer. A full SDLC end-to-end experiment is necessary if we're to understand the wide-ranging benefits this particular practice has. Remember, building software isn't just about writing code; our work isn't complete until it's in the hands of our customer.