2x MV1000, 1 VPN and 1 Adguard

Dear Friends!

I have purchased two MV1000 devices and set them up as 1x VPN Router and 1x Adguard device.
I have managed to configure them as standalone devices using the instructions from the website and they work well.

Now I would like to connect the Adguard device to the VPN device, in order to be able to access the internet with all PCs connected to the Adguard device through the VPN tunnel created by the first device.

I have to admit, that I am a total newcomer and I have no clue, how things really work. Somehow, I have managed to get through the basic configuration successfully, though.

I have no idea, how to configure the Adguard device to work together with the VPN device it is connected to and allow the VPN device to set the IPs for the PCs connected to the Adguard device.
On the Adguard device, I can not access the router functionality of the VPN device, as I have installed Ubuntu in order to get Adguard running.

Here is my full setup:

Fritzbox 7590, used as DSL modem, connected to MV1000 no. 1 (VPN Router) via WAN and static IP.
MV1000 no. 1 sets up an own network with a new IP range (DHCP). Here, I can connect my PCs and acces the internet through the VPN cliemt created on this device. This works well.

Now, I have added MV1000 no. 2 with Adguard installed, connected to MV1000 no. 1. I would like to leave the management of the network at the VPN Router and just re-connect my computers to the MV1000 no. 2 with Adguard. This way, I could use the adguard filter to check the traffic coming to my connected computers through the VPN of MV1000 no.1

Could anybody please help ?

Best regards,