How to downgrade from 400 to 100 MP2

I have had my MP2 trying to downgrade for 20 mins and it gets louder and then gets quite, like it's trying to install the software or downgrade the software, I don't see a status bar that shows progress in any form, Am I doing something wrong?

Nope, Assist 2 is a piece of shit..
I had v000.000.00 on my mavic 2.
I did an upgrade to v01.000.04 (latest version).It was allowed immediately.
Then I did a downgrade to v01.000.02 with DJI Assist2.
Then , since Assist doesnt allow to downgradeto v01.000.01 I used NLD app to downgrade from V01.000.02 to V01.000.01. It all went nice.
Then as I was in the correct version for patching I did NFZ,FCC and Sport+.
Everythinh went fine.
Notice: NEVER use patch on v01.000.00 or your mavic 2 is bricked... I did that and my drone was over.. had to pay 130€ usingDJI care refresh to get a new one..
They sent me a new one and then I have done it all over again to v01.000.01 and now everything is very nice pached and working :-)