Good evening,
I got an old “RouterBOARD 951 2n” updated to RouterOS v6.45.6 and I have the following network architecture.

I’d like to reach the 10.0.0.0/24 network from the network behind the MikroTik router (192.168.88.0/24) but the rest of the traffic should go directly to the internet. Unfortunately I have no idea how to set the routes and firewall rules.
Current state:
I have set up the OpenVPN connection and it works, but I can not ping for example 10.8.2.1.

On the OpenVPN server the following IPTables rules are defined:
Inbound:
-A FORWARD -s 10.8.2.0/24 -i tun2 -o eth0 -m conntrack --ctstate NEW -j ACCEPT
Outbound:
-A FORWARD -s 10.0.0.0/24 -d 10.8.2.0/24 -i eth0 -o tun2 -m conntrack --ctstate NEW -j ACCEPT
tun2 is there, because I have two other OpenVPN instances. They work perfectly with a regular client.
On the pfSense firewall the following static routes are defined:

Can somebody help me please. Thank you!