We have a square node, but node A never joined, can we bounce him and do a triangle? Or disband and rejoin as a triangle?

Which one is it? I can look and suggest!

Never mind, I found it: https://lightningnetwork.plus/swaps/21664
We can remove A and then the last participant will open to you. Is that OK?

So:
A->Deleted
B->new A
C->new B
D->new C

21644 is the agreement 

That works for us, yes, thanks 

OK, updated!

Awesome!!!