Before v2.4, you would find a chest that, when clicked with the key, would grant you the badge. There are two ways of getting the badge in your situation:

A. WIPE YOUR SAVE DATA and beat Garr7C again, then manouver your ship to find an entrance behind one of the ship spawners and touch the crate in there. Then, I think you can recover your progress by entering and exiting the cheat temple. [NOT RECOMMENDED]

B. (you will need the key for this) Make a backup of your save file, it should be in %Appdata%/garn47 Open Garn47 v2.3.5Again with your save file, go near the entrance for the sewers and click the chest you find there.

Or, if you like to cheat, try this:

Close your game, then open the file %Appdata%/garn47/saveData.garnular with a text editor. In here, find this in the text file:

"A7C": false,

Then, replace it with this:

"A7C": true,

Finally, save and close.