You work with Flexible Workflow for Purchase Contract.
Change of purchase contract during approval is not possible. But it is possible to change the released/rejected contract.
In this case there is a logic; checking what was changed in the contract. This is by comparing the changed fields with the fields of a reference structure.
In the App Manage Purchase Contract, there are 4 relevant fields which are editable, so changes on them will retrigger the workflow.
These are the relevant fields which retrigger the workflow based on the document type
Validity end date - Quantity & Value Contract
Material Group - Quantity & Value Contract
Target Quantity at item level - Quantity Contract
Target Value - Value Contract
KBA , MM-FIO-PUR-SQ-CON , Fiori UI for Manage Purchase Contracts , Problem