IP between L2L IPSEC

Hi,<br/>
<br/>
Apologies if I'm posting this on the wrong section, Admins please remove if you need to.<br/>
I should also mention that I'm not an IT expert.<br/>
I have the following issue, I have my PBX at HO sitting on VLAN2 172.172.1.10 I would like the phones on other location to get an IP same as HO.<br/>
As image shows below, I would like to have the phone located at VENUE with IP 172.172.34.5 to have an IP of 172.172.1.xxx<br/>
I remember doing it once but can't remember how.<br/>
Please let me know if you need more details.<br/>
<img src='https://octabit.com.au/images/pic/VOIP_VLAN2.jpg'/>