How do I move stock from one warehouse to another in Aicountly Inventory?

Use a Stock transfer document. In Aicountly Inventory it is listed under Adjust stock in the menu, described as moving stock between two warehouses. You can also reach it from New document, which lists every document type you can raise.

Create the transfer, choose the items and the source and destination warehouses for each line, and save it. The document then appears in the Documents register under the type Stock Transfer, where each line shows the movement from one warehouse to the other.

If you do not see Stock transfer in the menu, your profile probably does not have permission to create it; ask your company administrator.