Rerouting and forwarding traffic from VPN to WiFi

I'm new to Linux. I have set an **OpenVPN server** on one of my Raspberry Pi 4 running Raspbian system ([**PiVPN**](https://pivpn.io/) script). Then I set client OpenVPN on my other Raspberry Pi 4 (the first one server is at my parents' house abroad). I can easily connect both of them or my laptop or Android Smartphone and it all works fine. Recently I have set the client one as a **WiFi** hotspot so I can connect many devices and get IP from the Raspberry server (get around the geographical restrictions). Once I start the VPN connection I lose the internet connection over the WiFi (client Raspberry Pi). Yesterday, I got the USB-RJ45 Ethernet adaptor but over this, I get the same problem. I think I need to change routing and forwarding in the configuration.
Can anyone help me with it, please?