If you are new to Azure IoT Edge, I suggest to start with a MS Learn learning path. (or check out this MS Learn collection)
I do not see a MQTT client module in the Azure IoT Edge module market place. So I suggest building one yourself based on a MQTT Client library like this (This is a C# example but custom modules can be written in C, C#, Python, NodeJS, Java. Pick your weapon of choice).
If building a module is new to you, please check out the documentation (again multiple languages are supported). Examples of other custom modules are seen here.