while I was trying to configure the possibility of reaching management also through ethernet (PoE), I probably put the status of management on reserved. Now I can not access one of the two bridges. Do you have an idea on how to solve?
It sounds like you're trying to enable in-band management over the PoE port. To do this you'll need to add an ETH1 service point to the MGT service. Once you do that you will be able to manage the local 820S from ETH1. In order to manage the 820S at the far end of the link you need to add a radio service point to the MGT service. When you add the radio service point, be sure to include a C-VLAN tag. If you don't include a C-VLAN tag on the MGT radio service point, you will not be able to manage the far end of the link over the air.
Below are a couple screen shots showing what this should look like. I hope this helps, but if not please contact our Customer Support team at support.cambiumnetworks.com.