Child to parent updation using Master- Detail relationship.

Child to parent updation using Master- Detail relationship. Not possible workflow, Only possible on Trigger.

Ex:-
---
trigger OpportunityStageUpdate on Opportunity (after update) {
 //create list of Opportunity IDs
    List < ID > oid = New List < ID > ();
    //find Opportunity to add to list
    for (Opportunity o: Trigger.new) {
        if (o.StageName== 'Closed Lost') {
            oid.add(o.ID);
        }
    }
    List < ProfessionalServicesRequest__c> PSRUpdateList= [SELECT Id,Status__c from ProfessionalServicesRequest__c WHERE Opportunity__c in : oid];
   
    for (ProfessionalServicesRequest__c objPSR: PSRUpdateList) {
        objPSR.Status__c = 'Request Cancelled';
    }
    update PSRUpdateList;
}