Why can't I update superuser su binary though my device is said to be rooted properly?

[AC Question]

i cant update superuser su binary though my device is said to be rooted properly

i rooted my device. i installed superuser su but i cannot update the binary. i checked with root checker and it says i have proper root access. i cant go to recovery mode coz it does not show recovery option on button pressing. what is the problem ?
device ; lava iris x1