Openhabian 3.0 RC2 migration/upgrade not working

I don’t understand, please help. I did not understand how to upgrade.

i don’t know how you are using mqtt. What is your usecase?
First step is to install the new binding.

Bindings - mqtt install.

I already installed mqtt

Another option would be to run mqtt1 in OH2 and link it to OH3 with the remoteopenhab binding.

Presumably you have configuration files. Use this guide to convert:

I can not find any explanatory information for those who do not know. There is no document detailing the transition from Mqtt1 to Mqtt2. Please, I ask the knowing friends to make detailed documents. There are other people like me who have other problems.

Did you click the link provided? It takes you directly to the part of the document called Converting an MQTT1 installation - you might say it is a “document detailing the transition from Mqtt1 to Mqtt2”…

It explains the link conversion you say. I’m asking how to change mqtt2 usage instead of mqtt1.