Have a text object called dc_xxxxx_input or something you think makes sense for easy code readability. Also make a form button that matches whatever naming scheme you're using but _button at the end. Then use the following Event code:
dc_input_xxxxx_btn -> On clicked
Then add a sub-event of:
dc_xxxxx_input -> Compare text
Set the compare value to be "325".
Then, add the success events you want to happen. Also add an Else for if it fails and you have fail events. If you wanted to keep track of the correct codes, such as if the player can discover the code, it should be in a text instance variable for the dc_input_xxxxx_btn, and instead of doing the dc_xxxxx_input -> Compare text, you want to instead do:
dc_input_xxxxx_btn -> Compare instance variable
Then check if dc_input_xxxxx_btn is equal to dc_xxxxx_input.Text, then have success and fail events.