

Tutorial:
1.Fill your first slot up with an item it can be any slot in your Inventory, crafting table, chest etc, But to make Things Easier, use your first slot with an easy item. dirt, Cobblestone, sand etc. And also use a high amount number like 45 +

Lets Say you Filled up your 1st slot with 58 Cobblestone
2.The Tool should Look the same. In the "Items" list select your item, witch in my case is Cobblestone then Enter the "amount" - "58" in the Amount textbox then click the "Find Offset" Button
Here you see it Searching for the offset:
While its searching, do not use, place, open anything.
Search range is 34000000 - 38000000 And Search times vary. Longest search 30 - 40 sec's but id say around 60% of the time its a fast search

A Massive Thanks to BadChoicesZ For Adding the Search Function/Method.

3. Cool so we have found the offset, From here you can Check the offset, change the amount "255 is max" and also change the item.
I'm going to change mine to 255 of block of Diamond and click "Set All". as seen here:

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