For this particular achievement you will need to equipment any of the times bricks the quickest Red Brick is of course x2 which can be found during Chapter 3 - Go Directly to Jail.
Once you have gained access to the prison and unlocked your new ability of Chase McCain (Robber), you will progress and work your way through the cell rooms.
On the far left you will see the Red Brick and need to break the wall to gain access images shown below of Red Brick in cell.
Once you have picked up your Red Brick, you will have to complete the level first to equip it.
To do this press the START button scroll down to EXTRAS and select, now scroll down to Red Brick 12: which is now available and select each with
to turn on.
Now continue with your next Chapter to collect as many LEGO studs as possible and you will easily unlock the LEGO CITY HERO!
As soon as you have filled your bar the achievement will pop in game unlike the other Lego games, when you will hear that magic pop, achievement unlocked! (Credit to HolyHalfDead of when the cheevo pops)!
*Hope this helps if you have any issues please message, please be aware your x red bricks may need activating each time you close down game as I am having this issue just keep an eye out*