If you have used "Cart Lock", customer's will not be able to change their ordered items
It is up to you if you want to allow changing of ordered items
To add or remove items. go to "Order Management" > "Pending Orders"
Click "Edit Cart"
From here, you can edit customer's cart details
If your customer's order is already in "Pending for Verification", it means that they have already completed the order.
To edit their order, you can reject the order and get customers to use the same link to complete checkout again