Joining a whatsapp call after "Missed group voice call"

How do I join a call in progress, after being late to pick up the call, and getting a "Missed group voice call" notice? I tried calling back the call initiator, and she was presented the choice of ending the call in progress and then picking up my call, or continuing the call in progress and rejecting my call.

I've been used to doing this with the standard "Phone" app, which gives me three choices:
(1) pick up the new call and end the call in progress
(2) pick up the new call, putting the call in progress on hold, and then join the new call to the call in progress
(3) reject the new call, continuing the call in progress.

Anyone know how to (2) for whatsapp?

I'm running WhatsApp version 2.20.194.16, Android 7.0, Samsung Galaxy J3 Prime.