The Workshop Canister is located in the center of the game's biggest area - the Polymer Plant. To access it, you'll need to make your way through the level and solve a few puzzles. Here's how to get the Workshop Canister in Atomic Heart.
First off, you'll need to find the console at the center of the room. When you interact with it, you'll be presented with a grid of valves. Your goal is to turn the valves in the correct order to unlock the door to the Workshop Canister. You'll know you've done the right combination when the tubes housing the pigs, cows, and chickens turn green. To get the correct order, you'll need to refer to the square picture located right next to the console.
Once you've adjusted the valves in the correct order, you'll be able to proceed through the door to the next area. Here, you'll find a hallway with large fans on the ceiling. Make your way up the stairs on the left side and you'll eventually reach the control room. Inside, you'll find the Workshop Canister.
To activate the Workshop's power, you'll need to rotate the dial in the bottom left to make the center part blue. Then, turn the upper-center dial and press the red button to reactivate the power. This will give you access to the Workshop Canister, where you'll be able to craft some of the items needed to repair the environment.