Switching from Tier2 General to PBS Dependent Visa

Hello,
I want to switch my Visa from Tier2 General to PBS Dependent, since my husband has Tier2 General. I have resigned on 1st January 2020 and have indicated my last working day as 31st Jan 2020.
Can you please advise on below points:
1. Do I have to inform UKVI about my resignation- if yes, what is the procedure/ contact details.
2. Will my employer inform UKVI about my resignation, if he doesn't inform then what happens?
3. Is it mandatory or essential that my employer have to inform UKVI before I apply for visa switch.
4. Can I start my PBS dependent application before receiving curtailment letter from UKVI (60 days letter).

Your feedback will be highly appreciated.

Many Thanks!
Ragini

Switch as soon as possible, when eligible. No need to wait. No need to resign, unless employment was prohibited under PBS dependant status.

Thank you vinny, much appreciated.