RE: How can I change my inventory asset account from 12100 to 1350?
If you mean that your current default (special) inventory account is the 12100 account, the default every time you create a new inventory item, then...
To change the default account to 1350, and have the sub-account structure you've set up under it be sub-accounts of the special default account...
1) Edit each of the 1350 accounts sub-accounts and make the parent the 12100 account.
2) Edit the 1350 account and change its name to match the 12100 account: "Inventory Asset". When QB prompts you to merge the accounts, say yes.
3) Edit the 12100 account and rename and renumber it to suit: Likely, 1350 - Inventory.