How to uninstall hmmpress from my conda environment?
This time conda uninstall hmmer in the root environment did the job. The sequence of commands that led me there is shown below. Thanks Devon Ryan.

conda list | grep hmmer
hmmer                     3.1b2                         3    bioconda

conda uninstall hmmer
Solving environment: done

## Package Plan ##

  environment location: /Users/user/anaconda

  removed specs: 
    - hmmer


The following packages will be downloaded:

    package                    |            build
    ---------------------------|-----------------
    conda-4.5.9                |           py36_0         626 KB  conda-forge

The following packages will be REMOVED:

    barrnap: 0.9-0        bioconda   
    busco:   3.0.2-py36_6 bioconda   
    hmmer:   3.1b2-3      bioconda   
    prokka:  1.12-3       bioconda   

The following packages will be UPDATED:

    conda:   4.5.8-py36_1 conda-forge --&gt; 4.5.9-py36_0      conda-forge
    openssl: 1.0.2o-0     conda-forge --&gt; 1.0.2o-h470a237_1 conda-forge

Proceed ([y]/n)? y


Downloading and Extracting Packages
conda-4.5.9          |  626 KB | ################################################################################################################# | 100% 
Preparing transaction: done
Verifying transaction: done
Executing transaction: done


Checking that hmmpress is not available anymore:

hmmpress
zsh: command not found: hmmpress