Understanding OS Errors in the conda Command

We use anaconda to handle python environments.
When I tried to downgrade some libraries on shell, I entered the following command:

conda list

An error has occurred.

The error message is as follows:

OSError: libiconv.so.2:cannot open shared object file:No such file or directory

I tried to find a solution, but it didn't work.
I'm very sorry, but if you know how to solve this problem, please let me know.

• python 3.6.8
• Ubuntsu 16.04 LTS (Xenial Xerus)
• anaconda 4.7.5