Servo42D/57D supports position mode and Speed mode. On Position Mode, the Position Mode includes absolute position and relative position. 

The code below shows the Relative Position motion baccording to pulse number (page 78 on CAN User Manual)

#define SERVO42D_SPEED_MODE 0xF6

void Servo42D_RunPosition(void)
{
  TxHeader.StdId=SERVO42D_ID;
  TxHeader.ExtId=0;
  TxHeader.IDE=CAN_ID_STD;
  TxHeader.RTR=CAN_RTR_DATA;
  TxHeader.DLC=8;
  TxHeader.TransmitGlobalTime=DISABLE;

  TxData[0]=SERVO42D_POSITION_MODE1;
  TxData[1]=0x00;
  TxData[2]=0x3C;
  TxData[3]=0x02;
  TxData[4]=0x00;
  TxData[5]=0x00;
  TxData[6]=0x64;
  TxData[7]=(SERVO42D_ID+TxData[0]+TxData[1]+TxData[2]+TxData[3]+TxData[4]+TxData[5]+TxData[6])&0xFF;


  if(HAL_CAN_AddTxMessage(&hcan,&TxHeader,TxData,&TxMailbox)!=HAL_OK)
  {
    Error_Handler();
  }
}