Create conference with 2 existing calls

[chrischevy]

I know how to create a conference by calling Person A, press Conference, call Person B and press Conference again.

However, this scenario is not good all the time. Let's say I receive 2 calls, and I need to create a conference, I can't do it...

How can I create a conference by merging 2 existing calls without pressing conference before placing the second call ?

Not sure if I'm clear

I found these instructions but they don't work (there is no "Send" or "Select" button at step 4). I just keep switching between calls

Joining Two Calls in a Conference
You can select a hold call to join into a conference call with the active call.
Procedure
1. Place two or more calls using the same or different accounts on the phone.
2. Select the desired call for conference and ensure that the call is active.
3. Press Conference (Conf).
4. Select a desired hold call, and then press Send.
On the SIP-T48S/T48G IP phone, tap the desired hold call from the left sidebar.
On the SIP-T42S/T42G/T41S/T41P/T40P/T40G IP phone, press Select.
The active call and the selected hold call are joined into a conference. If there are multiple hold calls, the other hold
calls on the same or different accounts remain hold