Explain what Convert from MSB to LSB means.
Here you want to reverse bytes, which is equivalent to convert from big endian to little endian

LSB(least significant bit) convention is used, all hashes must be converted from MSB to LSB

This feature is confusing. Which hash must be converted to LSB? inputs? ouput? A each reduction step?

'LSB(least significant bit) convention is used, all hashes must be converted from MSB to LSB'

Could you explain what does this sentence means ? How should I understand it ?

So hashes, which are passed to function are in MSB convention? And they should be converted to LSB before concatenation?