How can I change a unit price I have entered incorrectly?
If you have set your material's unit price on the Add Material form, this information is saved as the material's Starting Adjustment, along with the quantity entered in the same section.
To change this unit price, you'll want to edit your Starting Adjustment by following the instructions in this help article: How do I edit a Material Inventory Adjustment?
If you have entered an incorrect unit price via a Material Expense, you'll need to locate and edit the expense (How do I edit an Expense?). Once you have made the changes, your material's unit price will be automatically updated for you.