Update DFF using Groovy

Summary:

We are trying to update a DFF on contract on set of another lookup type field using triggers. Simple setattribute using the field name found in groovy Fields list doesnt work.

eg TotalValue.contractheaderflexfield..?= '100' doesnt work and not even the setattribute..

Any ideas to make this work ?

Content (please ensure you mask any confidential information):

Version (include the version you are using, if applicable):

Code Snippet (add any code snippets that support your topic, if applicable):