1. register here — https://accounts.2k.com/
2. authorize here — https://portal.2k.com/2k/portal/connections
3. Get More Content — scroll down to and install «Multiplayer Compatibility pack»
4. Re-start game client
5. Login in 2k account in Civ 6 game — bottom right corner, icon 2k

If doesn’t work in «Get more content» — restore purchases.

If doesn’t work — look for help in the Internet. Sorry.