critor wrote:Just drag the .tcc file to the TI-Nspire documents browser.
After your suggestion I remembered there was a specific option into Computer Link menu ('Instruments' -> 'Install SO')
This morning I was able to full downgrading to 3.6.0.550
And now installed correctly Ndless 3.6 following the guide https://tiplanet.org/forum/viewtopic.php?f=57&t=14087, thanks critor for having led me to success