trigger AccountReplicate on Account (after delete, after insert, after update) {
        if ( trigger.isInsert ) {
            for ( Account acc : trigger.new ) {
                AccountOne__c ac = new AccountOne__c();
                ac.Fax__c = acc.Fax;
                ac.Phone__c = acc.Phone;
                ac.Name =acc.Name;
                insert ac;
            }
        }
        
        if ( trigger.isUpdate ) {
            integer  i = 0;
            list<AccountOne__c> a2 = new list<AccountOne__c>([SELECT Id 
                                                           FROM AccountOne__c 
                                                           WHERE Name =: trigger.old[i].Name ]);
            for ( AccountOne__c c1 : a2 ) {
                c1.Name = trigger.new[i].name;
                c1.Fax__C = trigger.new[i].Fax;
                c1.Phone__C = trigger.new[i].Phone;
                i++;
            }
            update a2;
        }
    }

I tried bulk trigger for the update operation, but it's not working can anyone help me?