The Happy Birthday tape is located in the main house attic in a locker. Here are the steps to solve this tape, do this step really quick for the 5min limit.
If you want you can skip telescope steps 5-7 and use the code directly. Is always the same code (chainsaw man – raven on hat – baby)
Step 1: pick up candle from the mannequin , walk to cake room and listen to Lucas
Step 2: turn on the stove and light the candle
Step 3: go to the door with the rope and cut through the rope with the candle, pick up the empty balloon in this room
Step 4: use the balloon at the pipe (gasleak) in the wall near the stove and you get the quill pen
If you are too slow or want a little bit time saving you can skip this 3 steps and you can directly go to step 8Step 5: go to the toilet, use the toilett and pick up the dirty telescope
Step 6: clear the telescope at the passage to the cake
Step 7: use the telescope and look to the monitoring system, you will see a code (chainsaw man – raven on hat – baby)
Step 8: use the code inside the cake room and pick up the straw doll and also the winding key from the keg
Step 9: use the straw doll at the stove and you get the dummy finger
Step 10: Put the dummy finger, quill pen and window key on the mannequin where you got the candle
Step 11: go to the room where you got the balloon and enter the code LOSER, pick up the valve handle in the next room on the wall
Step 12: use the valve handle at the pipe in the cake room
Step 13: Light up the candle at the stove and put it on cake