Write down the ASIN

Go to your Seller Central home page. Go to the menu on the top left. Click on Inventory -> Manage Inventory

On the right of the page, click on "Add a product"

There is going to be a white rectangle box in the middle of the screen where you can enter in the ASIN that you wrote down. Pull up the ASIN you wrote down and type it in the white rectangle box. Click on "Search".

Your product should come up. On the right of the product click on the area that says "Select a condition". Select "New". (I am assuming that you are selling new products).

Click on "Sell this product"

The first thing you should do on this screen is type in the new SKU that you want for the ASIN. It will not be highlighted so it seems like its not a requirement and its easy to forget that you need to put in this new SKU.

Fill out the rest of the information such as price, listing price, and that you want it to be fulfilled by Amazon. Once you have filled everything out, click on "Save and finish" at the bottom.

You will now have to fill out extra information such as dangerous goods requirements but at the bottom you can click on "List as FBA and send Inventory". At this point, it should all be very familiar and straight forward. You will be sending FBA units for a new offer you have created with a new SKU but the same ASIN as you requested.