Can any one help me with the update operation
​​​​​​​public class AccountUpdateWithDelegated {
public static void fillDelegatedApproverEmail(Set<id>  accn) {
List<ProcessInstance> pi = new List<ProcessInstance>();
Map <ID,ID> prinst =new Map<ID,ID>();
Map <ID,ID> Prsinswi =new Map<ID,ID>();
Map <ID,ID> userndelegated =new Map<ID,ID>();
List < Account > ac = new List < Account > ();
pi=[select id,Status,TargetObjectId ,LastActorId from  ProcessInstance where  TargetObjectId IN :accn];

for (ProcessInstance ps : pi){
prinst.put(ps.TargetObjectId,ps.id);
system.debug('list of id '+prinst);
}

List<ProcessInstanceWorkitem> piw = new List<ProcessInstanceWorkitem>();

piw =[select id,ActorId,ProcessInstanceId from ProcessInstanceWorkitem where ProcessInstanceId IN :prinst.values()];
for (ProcessInstanceWorkitem psiw :piw){
    Prsinswi.put(psiw.id,psiw.ActorId);
    system.debug('list of process instance items in piws'+prinst.values());
}
 
List<user> us = [select id,DelegatedApproverId,Email,createdbyid,isactive from user where DelegatedApproverId!= NULL and ID IN :Prsinswi.values()];

system.debug('Delegated approver '+us);
for(user usrs :us){
userndelegated.put(usrs.id,usrs.DelegatedApproverId);
    system.debug('set of delegated id '+userndelegated);
}
List <user> us1 = [select id,email from user where id IN:userndelegated.values()];
for (user usrss : us1) {
            Account acce = new Account();
            acce.Delegated_Approver_Email__c = usrss.email;
            //acce.id = prinst.get.ps.TargetObjectId;
            system.debug('Delegated_Approver_Email__c' + acce.Delegated_Approver_Email__c);
            ac.add(acce);
        }
    If (!ac.isEmpty()){
        update ac;
    }
}
}

Can any one help me with the update operation