It's Not Yours, It's Mine is a mission in LEGO City Undercover: The Chase Begins.
Walkthrough[]
You have a long drive ahead of you transporting Natalia Kowalski to the sheriff station in Bluebell Woods. Drive here there and then stop in the objective marker. Drive to Blackwell Mines and then speak with the foreman there to learn about your next costume.
Make your way to the costume closet and open it up to get the Miner disguise. You can now smash boulders and do other various miner things. Head over to the entrance of the mine and use your Pickaxe to smash through the glittering boulders that are here. Once they've been smashed, you can move forward and enter the mine proper.
Fight the enemies here. Then go to the switch and pull it to change the "color" of the area. Switch to your Robber costume and use the Color Gun to get the new color. Shoot the nearby red switch this color to open the way, and then continue through the mine with your Miner costume.
Smash everything. You'll come to a stopping point, but it is bypassed by building a ladder. Climb up and fight all the enemies that are up here. Switch to the Construction Worker costume and smash a hole in the concrete. This will cause another water sprout to shoot up out of the ground. Stand in the water and then drop through the hole of the shack.
Still as the miner, defuse the bomb in the corner here. Then use the nearby switch to blow up the blocked areas of the mine. Go to the next objective marker so that you can exit the mine. Now just return to the mine foreman and report to him about your progress.[1]