Gotcha. My sympathies - I've been where you are. Well, to answer your original question, to adjust inventory, you go Inventory>>Transactions>>Transaction Entry and enter your adjustments there. Depending on how you posting settings are set, posting an inventory transaction MAY also affect your GL, since the modules are integrated. To prevent affecting the GL, if you don't want that to happen, go to Administration>>Setup>>Posting>>Posting, select Series=Inventory, Origin=Transaction Entry and uncheck the Post to GL and Post through GL Files checkboxes. That will prevent any transactions postinng to the GL. When you're done with your transactions, re-check the box(es) if desired.
Hope this helps. Welcome to the GP world and feel free to post as many questions as you need help with. We're a friendly bunch here.