This guide will walk you through the process of transferring the board from the OEM Subaru Key Fob to the Miniature Key Fob. NOTE: Take your time, and be patient. Do not force anything. This guide worked for my fob, but I do not claim responsibility for any damage yours incurs while following these steps.
STEP 1: Separating the OEM Fob Halves
Depress the square silver button on the back of the fob with your fingernail while simultaneously pulling on the key ring at the bottom. This will release the physical key from the fob. Only pull the key out about halfway.
While firmly grasping the metal sides of the fob in one hand, use the physical key as a lever by pulling straight down. This will separate the two halves of the fob.
The top half of the fob (with the silver trim) can be set aside, along with the button layer, and the rubber waterproofing gasket. Remove and set aside the physical key.
STEP 2: Removing the Board and Battery
Flip the bottom half of the fob upside down to dump out the board/battery combo. You can then set aside the bottom half of the fob.
UPDATE: BOARD VARIANT IDENITIFICATION
Subaru implemented a minor change to the fob design around the 2023 model year. The revised board is thinner. To accommodate this, Subaru added a "spacer" on the top side of the board between the silicone seal and the board. This spacer has tabs on it that sit over the four buttons to fill the space. If your board has this additional part, you should remove it as well. You ONLY need the board and the bottom bracket that contains the battery.
Please identify which variant you have, and be sure to order the correct version for your fob!
Pictured below is a photo submitted by a customer showing the added black spacer in the revised key fob.
STEP 3: Assembling the Mini Key Fob
Grab the board (sans the upper spacer if yours had one), and the bottom half of the new miniature fob. Orient the board so that the battery will be face down and towards the tab at the back. Lay the battery end down into the fob base, leaving a gap on the tab side, then slide it towards the tab, and snap the top into place.
Retrieve the physical key you set aside earlier, and remove the small ring loop. Then insert it into the curved slot on the top half of the fob. Note make sure it is fully inserted and sits flush. Be gentle handling the top half of the fob through the following steps to ensure it doesn't fall out until fully assembled.
Now take the two halves, and slot them together on the top side. Then place the fob down on a flat surface and firmly snap the bottom sides together. This can take some force.
STEP 4: Systems Check!
Make sure and test the four buttons to ensure you can feel them click. This ensures something didn't go wrong with the assembly, and that your board is compatible. You should be able to press the buttons, but it shouldn't be OVERLY easy to accidentally press them.
If you ever need to separate the two halves again, carefully slide a thin, wide object (such as a butter knife) into the horizontal gap just underneath the key ring at the bottom, and then carefully twist back and forth until the two halves snap apart.
Enjoy all that extra space in your pocket!