Can I update a particular field based on the incoming Request?
Yes, you can update a particular field using WorkFlow Assignment Values.
Goto Setup > Workflow Settings > Create a workflow rule.
Then create a workflow assignment value and associate that to the
Workflow Rule.
For detailed help to create workflow rule and workflow assignment value, refer Workflow Settings.
Example:
Let's assume you would like to assign Priority as HIGH when a "request
is coming from XYZ company" or "a particular field in your Request Form has 123 value"
To achieve this, Goto Setup > Workflow settings > Workflow rule.
Create a new rule > Select Request module > Criteria
mention "contact e-mail contains @xyzcompany.com or the field name contains = 123 value" and Save the Workflow
Rule.
Scroll down the workflow rule and you can find Add New Assignment Value.
Add New Assignment Value, select "Request" as module name and under
assignment values, select "Priority = High" & Request Owner as ABC Support Agent and save the Workflow Assignment Value.