MRP Area Customizing and Mass Updating

I have created my storage location as MRP area in the customizing. Now when I am trying to enter in the MRP 1 view in material master, it is showing the following error.
Error: MRP area is not assigned to Plant.
But in customizing I have assigned plant while creating the storage location as MRP area. 
To create storage location MRP area, do the following steps:
1. Create MRP area by SPRO -> MRP -> Master data -> MRP area -> Define MRP area.
Select MRP type 02 - storage location
2. Define scope of planning by tcode OM0E.
Insert your Plant.
3. In MM02 assign MRP area in MRP1 view.
4. In SPRO -> Define parallel processing in MRP.
5. While MRP run, select parallel processing in the initial screen.
If you want to run MRP only for one MRP area then only enter the MRP Area there or If you want to run MRP for Plant with MRP area, several MRP area you can 
select there.
Run MRP with MD01 then.
 
What exactly is the use of transaction code OM0E and What is the use of defining scope of planning.
In scope of planning (OM0E) :-  you can define:
1. Several plants
2. For One MRP area
3. Plant with MRP area
4. Several MRP area.
If you want to run MRP for a plant, you can enter a plant as normal.
But if you want to run multiple plant or other option, you have to create scope of planning.
So that MRP plan for Multiple plants.
Do you know of a program/transaction (like MASS) that will enable me to update Material master MRP Area data (table MDMA)? 
Try report RMMDDIBE
- Fill in the MRP Area Data
- Fill in the Forecast Data