In order to dress the doll more easily, the hand part has been designed to be easily separable. 
You dress the doll as follows: 

1. Hold the hand part and the arm, including the wrist inlet, with both hands, one for one.

2. Hold the wrist inlet in a fixed position and pull the hand part out.  The tension part will come out.

3. Hold the tension with the hand that was holding the wrist inlet, and separate the hand part from the S-hook.

4. Put the hand part down and insert the S-hook into the groove of the wrist inlet.

5. Dress and pull out the S-hook, and the tension will come out.  

6. Insert the hand part into the S-hook again, and replace the tension string.