Hi Kimia,
I don't understand the need for the command " conda install -c conda-forge conda"
To install Ubermag/joommf follow the instruction manual.
If you find it difficult to follow, you can watch the installation video on Youtube.
They have 3 videos for Windows, MacOS and Linux.
Youtube Channel name: JOOMMF Channel
You can view based on your requirement.
Hope this helps.
Regards,
Ponsudana