To create a commitment change order.
In Procore, purchase orders and subcontracts are called commitments. A commitment is a contractual agreement between a buyer (for example, a project owner, a general contractor, or a specialty contractor) and a seller (for example, a contractor, a subcontractor, or a vendor). The seller is responsible for completing project work or fulfilling an order for the buyer. When you need to alter the terms of the original agreement, you can create a commitment change order.
When the Change Events tool is enabled on a project
The process that you will use to create a commitment change order in Procore depends upon a few factors. First, if the Change Events tool is disabled on the project, you will use one of the processes below. Also, keep in mind that the number of steps required to create a commitment change order is dependent upon the change order tier setting that is configured on the project's Commitments tool. See Configure the Number of Commitment Change Order Tiers:
Although not recommended, Procore also supports a 3-Tier configuration:
If you have created a purchase order or a subcontract and need to alter the terms of that item, use the steps below to create a commitment change order.
If the Change Events tool is enabled on your project, the Create Commitment CO button is not available. Follow these steps instead:
If there are costs associated with the change order, add line items to the change order's Schedule of Values (SOV). 
For Companies That Have Enabled the ERP Integrations Tool
After the commitment change order is placed into the 'Approved' status in the Commitments tool, project managers will typically send the change order to the ERP Integrations tool where it must be accepted by an accounting approver for export to the integrated ERP system. For instructions, see Send a CCO to ERP Integrations for Accounting Acceptance.