Looks like you have no LAN ports in the rooms and you are using wireless backhaul. TP-Link Archer BE230 is a low end dual band EasyMesh node and it is a poor addition to the EB810v, if you need to use wireless backhaul. But if you have LAN ports in the rooms, then maybe there are better setup using Ethernet Backhaul to suit your needs.
Anyway, since you have already bought the Archer BE230, please post the floor plan (with details of the locations of the ONT, main EB810v and Archer BE230, as well as LAN ports in the rooms if any) to see how to optimize the placement of the main EB810v and the Archer BE230 node.
In general, the mesh node needs to have good connection to the main nodes, two walls in between the main node and the mesh node is a NO-NO. Best is to have line of sight with no walls in between. Depending on the situation, you may be okay with one wall in between the main node and mesh node.
Often people think that it is good to put the wireless mesh node (or repeater) to the room with weak signal, that is usually the worst choice.
More about TP-Link EasyMesh
https://dongknows.com/tp-link-easymesh-wi-fi-system-review/
More about Mesh system in general
https://dongknows.com/mesh-wi-fi-system-explained/