LAN to WAN – 2 router question

Hi, I have setup 2 router LAN to WAN installation. 192.168.1.1/24 is my Public Facing LAN (for IoT’s) & 192.168.2.1/24 is my Private LAN.

I am able to ping any MAC address in Public LAN from Private LAN – no issues.

However, I want to access a specific (exception) MAC address in my Private LAN from a MAC address in my Public LAN. Can I do this? How? Any help would be much appreciated.