I do not know enough about that integration to know if it is configurable. The person making the integration should usually fix it. If they don’t, two things can be done about it: create a template sensor or try to overrule the things that are wrong using a Customize yaml file. Cursomize would be the first choice for me:
You need to at least override the unit_of_measurement, and possibly also the device class (temperature). You can see what they are by looking the entity up in the developer tools, status tab. When it is correct, it should look something like this:
I’m not sure changing it in the top part of developer tools itself (where you can set the state) will survive a reboot, but it is a good place to see what is set. As far as I know you need to have the customize section or include file in your configuration.yaml to make the actual change, as described in the documentation I referenced.
Or did you change the device class from the entity settings page (you can reach that from developer tools as well). That will work, but it does require a supported unit_of_measurement. If you were able to do it from clicking the i symbol in the developer tools, and then the cog, that is a supported way to change it. You do not need the yaml file for that.