Is a static route the solution?

Dear experts

While I'm actually a software engineer and not a network engineer, I'm requesting your help. :-)

• Setup:
  - Router 1, connected to my ISP (WAN) 192.168.192.1/24
  - Switch, port based VLAN
  - Router 2, EdgeRouter Lite, eth0 (WAN, internet) connected to router 1, 192.168.192.21
  - Router 2, EdgeRouter Lite, eth1 (LAN) connected to router 1, 172.16.4.1/22, DHCP
  - Router 2, EdgeRouter Lite, eth2 (LAN) connected to router 1, 172.16.8.1/22, DHCP currently not in use
  
  
• What's ok:
  - Clients connected to router 1, no problems
  
  
• Problem:
  - Clients connected to router 2, no problems to access internet but can't connect to network 192.168.192.0/24 on router 1

I've tried to setup static routes but obviously I'm doing something wrong... :-(
Well, at least I was able to plug it in to my power socket.

Cheers Mike