If you met the situation as showed above, please try below steps:
1. Please open the camera case and clean any possible dust particle on the below circled parts. Otherwise it will make the sensor board slant, not just right vertical to the lens.
2. Clean the dust on the sensor board, inside the camera case and both ends of the lens.
3. If it is still blurry, please add 1-3 layer of tapes to the corresponding side to make the sensor board levelled.
At last, you may twist the lens to check the focus and fix it with the lens ring.