The first tiebreaker is points.
If tied for two teams,
1. Most head-to-head wins
2. Most head to head goals scored
3. Most head-to-head away goals scored
4. Better goal difference in 6 group matches
6. More goals scored in 6 group matches
If 3 teams are tied, the matches involving the 4th team (who obviously must be 1st or 4th confirmed) are omitted and the three are looked as a mini-group
1. Most points in the games
2. Better goal difference in the games
3. More goals scored in the games
If the tie is broken for only one team then the 2 teams criteria apply for the other two teams.