Movement/adjustment should be reverse of probe offset change

Marlin/Marlin_main.cpp

@@ -7984,7 +7984,7 @@ inline void gcode_M503() {
           if (diff) {
             for (uint8_t x = 0; x < GRID_MAX_POINTS_X; x++)
               for (uint8_t y = 0; y < GRID_MAX_POINTS_Y; y++)
-                bed_level_grid[x][y] += diff;
+                bed_level_grid[x][y] -= diff;
           }
           #if ENABLED(ABL_BILINEAR_SUBDIVISION)
             bed_level_virt_interpolate();
@@ -7993,7 +7993,7 @@ inline void gcode_M503() {
 
         #if ENABLED(BABYSTEPPING)
           if (planner.abl_enabled)
-            thermalManager.babystep_axis(Z_AXIS, lround((value - zprobe_zoffset) * planner.axis_steps_per_mm[Z_AXIS]));
+            thermalManager.babystep_axis(Z_AXIS, lround(-(value - zprobe_zoffset) * planner.axis_steps_per_mm[Z_AXIS]));
         #endif
 
         zprobe_zoffset = value;