Reverse shell from behind firewall and NAT


I have been working on a cyber security project in which I placed a web server behind ipfire router ( external IP 192.168.44.3). This is part of a GREEN LAN network (say IP IS 192.168.33.11). I am trying to get a reverse shell from this target web server to my attacker machine kali (ip 192.168.44.5). CAN somebody help me in detail as how to get this reverse shell successfully?