You can do an Inventory Adjustment here:
The adjustment will have to happen location by location - not all in one go.
This method uses a spreadsheet so it's more suited if you want to change the stock of many products in one go.
For individual product changes, you can also follow these steps:
Upon clicking on e.g. mango you'll be able to reach this:
You can then change the quantity by adjusting the Physical Count Quantity field. You'll still need to create an Inventory Adjustment document:
Of course, issuing documents also changes the stock - it is this that you should always try first.