Help to understand heating configuration

Good evening.

I am a total beginner and I am confused.

I am trying to set up a smart heating configuration. What I don´t understand is wether I should configurate the thermostat via the fritz box or via home assistant.

In the fritz box I already have the option to set temperatures for the whole week and I don´t know how to disable the whole function. (there would be two devices sending commands otherwise or is home assistant overwriting the router?)
Of course I want to be able to use all the functions in home assistant and not only just see the diagrams of the temperatures. Do I need another Intergration or Add-on to be installed in home assistant or how do you use your thermostats?

My configuration is the following: raspberry with home assistant, Fritz box as router and my smart heating thermostat is a Fritz Dect 301. I had no problems with discovering the devices.

Thank you for you help!