For example:

• https://gtm.you1.cn/groups/DerankersDerank (one of the biggest groups i know)
  
• Help me fill this list <3

You can find the player code ingame on the main menu. Expand your lobby overview and go the mail-symbol that says "friend requests".

Then click on the "add friend" symbol and copy your code.

Every Group has a chat-room where you can chat with other group members. Go there and post your code.

If you are having prem8s which are also willing to derank, you can write something like "+2" if you are already 3 or "+3" if you are already 2.

You could also specify the ranks you want to derank with, because the highest rank usually deranks faster then everybody else.

Usually you derank by disconnecting, because its the fastest, so you could write "dc only" as well. So everybody knows, how you wanne derank.

To let others know, you are full, just delete the message.

Before you join a competitive match, make sure everybody knows how to derank by dc.
You probably derank faster with short matches, but i still have to test this. Further updates coming

You have to wait till the warmup is done. There is no way around this :(

You need to make sure, that on the first round, only one of you disconnects first (for 10 seconds). That way you dont need to wait for the technical timeout (2 minutes).
After that first player reconnects, you can continue with the next step.

Everyone of your team take a timer (on your phone i.e.) and set it to 2 minutes or less, so you know when to reconnect and dont get a cooldown for not joining within 3 minutes. Then everybody disconnects.

When the timer is ringing, you can reconnect to the game and continue with the Step "Disconnect". Do this till the game is over. It should take 10 minutes max for a long match.