On this page of the FNAF Security Breach guide, you can find a detailed walkthrough for the Free Freddy mission. .
The mission begins with you sitting inside Freddy. After a short conversation, time to disembark. After begin scanned by an animatronic, you need to look through the parting in the curtains.
Now, go back to Freddy and open the gift that is in his stomach. You've received a Faz-Watch - an item that allows you to look through the cameras, and access the map, messages, or mission objectives. This item will be the backbone of further gameplay.
Look towards the door - to open it, press the button next to the arcade machine. Its location is shown on the screen below.
Behind the door you will find a technical corridor. At its end you will find a terminal where you can save the game for the first time. There are cardboard boxes to the right of the terminal You have to climb them to get to the ventilation shaft.
. Follow it to reach the museum. To find the Photo Pass, you have to go through the entire room and the gate at its end - right behind it you will find the gift with the pass you are looking for.
Once you get the Photo Pass, go back to the museum and go to the door to the room where Freddy is being kept. With this pass, you'll be able to open it and free the animatronic. After this step, the quest will end.