Navigate to "Function - Homing" on the touchscreen. Clean the stain on the surface of the upper part of the Z-axis plain shaft using dust-free cloth.
Clean the stain on the lower part of the surface of the Z-axis plain shaft using dust-free cloth.
Apply new grease to the surface of the plain shaft.
After the homing process, navigate to "Z-axis down" to lower the heated bed to the bottom. Navigate to "Z-axis Homing" again to apply the grease evenly.
Lower down the Z-axis. Clean the excess grease accumulated at the ends of the plain shaft.
Clean and lubricate the other 2 Z-axis plain shafts in the same way.