Seems like the "idler arm" is a problem area ... in fairness to Geeetech, the same thing happened on my Ender 3. There's been a lot of discussion on forum thread: "New A20M couple of problems" and some others as well.
Here's a link to page 2 of that thread:
viewtopic.php?f=108&t=69809&start=10
You'll see a post by jarda3d with 3 suggested designs (Thingverse) for printing the arm. I had success with the second one.
https://www.thingiverse.com/thing:3456879
Somewhere there's a recommendation of what to do if you have one extruder not working so you can print this part with the working extruder. It seems to not be a good thing to just leave the other entry port to the hot-end without something in it. I admit I just used my Ender 3 to print the idler arm.
I've been using my printed idler arm successfully for the A20M since my posting on Jan 9, 2020.
On the other hand, getting a factory replacement from Geeetech? Not so much success. Although I realize that it's a tough time for people in that region right now ... I'm happy if y'all stay well as you can and get back to me with a replacement part when things are more normal.
- Jay