I know this is an old topic, but nevertheless. You need to specify which sensor you are using in the RTIMUSettings.h file. A segment of the code will follow (from Arduino RTIMULib GitHhub):
// These are the local variables
int m_imuType; // type code of imu in use
unsigned char m_I2CSlaveAddress; // I2C slave address of the imu
int m_pressureType; // type code of pressure sensor in use
unsigned char m_I2CPressureAddress; // I2C slave address of the pressure sensor
// IMU-specific vars