🐛 E3V2 Mesh Viewer followup (#22850)

Marlin/src/lcd/extui/mks_ui/draw_preHeat.cpp

@@ -124,18 +124,22 @@ static void event_handler(lv_obj_t *obj, lv_event_t event) {
         else if (uiCfg.extruderIndex == 0) {
           uiCfg.curTempType = TERN(HAS_HEATED_BED, 1, 0);
         }
-        lv_obj_del(btn_pla);
-        lv_obj_del(btn_abs);
       }
       else if (uiCfg.curTempType == 1) {
         uiCfg.extruderIndex = 0;
         uiCfg.curTempType = 0;
-        lv_obj_del(buttonAdd);
-        lv_obj_del(buttonDec);
       }
-
       disp_temp_type();
       break;
+    case ID_P_STEP:
+      switch (uiCfg.stepHeat) {
+        case  1: uiCfg.stepHeat =  5; break;
+        case  5: uiCfg.stepHeat = 10; break;
+        case 10: uiCfg.stepHeat =  1; break;
+        default: break;
+      }
+      disp_step_heat();
+      break;
     case ID_P_OFF:
       if (uiCfg.curTempType == 0) {
         thermalManager.setTargetHotend(0, uiCfg.extruderIndex);