The backrest and the seat pan need to be lined up perfectly, and the backrest should be inserted into the end of the groove.
If you failed to insert the screws into one of the sockets, it is most likely that the backrest and the seat pan didn't line up properly.
Please check out the instructions below and try assembling once more.

1. Please disassemble all of the chair parts.
2. Find a flat surface and assemble both armrests on the chair first. You will have the seat + armrests assembled.
3. Place the seat mounted, and insert the backrest inside the seat pan.
* TIP : The armrests will help the chair stay tilted at the right angle.
4. Insert screws from following the numbered spots in the picture.
* TIP : Going diagonal helps easy assembly.
5. Before screwing the bolts, please make sure to press the joints very hard.
* TIP : In case it doesn't work, it is helpful to put up the seat side with a hand and push down the backrest while inserting the bolts.