To do this, please follow the below steps:
In [Inventory] [Stock Locations] click on the name of the required stock location where the item to be adjusted is.
Type the name of the Product in the highlighted field, as below, and [Search].
Click on the value in the [Unit Value] column, and a pop-up window will appear.
In the pop-up window, change the value to what the unit price should be and click 'Save'.
This will take immediate effect.