In order to ensure that your desired margins are met that you have established in the setup of the Pricebook, the option for technicians using the Tech App to alter the prices is solely allowed by applying a promo code.
You can create Promo Codes in your Admin Portal through the Promo Code report in the Reports Center.
Should you need to manually adjust the prices of tasks without applying a promo code, an Admin Portal user with Admin or Super permissions will have to perform the price override. Requiring this admin override will ensure adherence to your desired pricing for tasks by your tech staff and will allow for a faster quote building process as the technicians will adhere to the pricing built into the Pricebook.