Redirect after login

Hello. I have a microtik router connected to another router. The MT router has a wifi hotspot configured. What I want to do is to login on an external website and the redirect back to the MT router to gain access to the internet. I have managed to redirect the login to the external page but how do I get back in. I have a php script running and in the header I want to redirect. Configuration is: IP-public —> router 1 → 192.168.1.x → WAN port MT → switched ports 192.168.88.x and hotspot 10.5.50.x. Do I have to use port forwarding in router 1 or is there another way. Thank you in advance.