To obtain this achievement you need to win matches against the A.I with both Natalya & Bret Hart. Now when you begin the game Natalya is already unlocked, but for those who did not purchase the Accelerator DLC, which is included in the Season Pass and sold separately, will need to unlock Bret Hart by winning 90 matches against the A.I.
You can view your progress towards unlocking Bret Hart by going into "Options" from the main menu and then "Unlockables" and navigating through to Bret under which the screen will display your number of wins out of 90.
I have verified that despite the wording of the unlock requirements provided in the game that wins against A.I. in both the "Play" Mode and WWE Universe count towards unlocking Bret. Thus it is recommended that you get the bulk of your wins in WWE Universe en route to obtaining:
If you have completed all other achievements for playing in Universe or as other superstars you can always go into the "Play" menu and setup an easy to win match (finisher matches are popular) and continue to hit "Rematch" at the end of every match and it will continue to count up wins for you without you having to setup a new match with long loading times after each and every win.
The type of match you need to win with each superstar once their unlocked doesn't matter as long as it is against the A.I. Although I should note that while a mixed gender tag team match is a great idea that only the superstar you control at the time of victory (be it from pinfall, submission, etc.) gets credit for the win and thus you do have to do two matches, wining one with each Natalya & Bret, to unlock this achievement.