global Messaging.InboundEmailResult handleInboundEmail(Messaging.InboundEmail email,Messaging.InboundEnvelope envelope) {
        
        Messaging.InboundEmailResult result = new Messaging.InboundEmailresult();
        list<ProcessInstanceWorkitem> lstApprovalProcess = new list<ProcessInstanceWorkitem>();
        set<ID> setUserID = new set<ID>(); 
        String subToCompare = 'Approver';
        String strUSerID = email.plainTextBody;
        List<String> lstID = strUSerID.split('-');
        
         System.debug('lstID is:'+ lstID );
        if(email.subject.contains(subToCompare) && !lstID.isEmpty() )
        {
            for(ProcessInstanceWorkitem objProcessInstance: [Select  p.Id,
                                                             p.ProcessInstanceId,
                                                             p.ProcessInstance.Status,
                                                             p.ProcessInstance.TargetObjectId,
                                                             p.ActorId,
                                                             p.OriginalActorId,
                                                             p.CreatedById,
                                                             p.CreatedDate
                                                             from ProcessInstanceWorkitem p
                                                             where p.ProcessInstance.TargetObjectId = : lstID[0]]){
                                                                   if(lstID[1] != null && lstID[1] != ''){
                                                                    string appID = (lstID[1]).trim();
                                                                    if(appID.length() == 18 || appID.length() == 15){
                                                                        objProcessInstance.ActorId = appID; 
                                                                    }
                                                                    else if(appID.length() > 18){
                                                                        objProcessInstance.ActorId = appID.subString(0,18);
                                                                    }
                                                                }
                                                                 lstApprovalProcess.add(objProcessInstance);
                                                             }
            if(!lstApprovalProcess.isEmpty()){
                update lstApprovalProcess;
            } 
        }
        return   result;
    }
}

Could you please assit on this,