The easiest way is with pip:
pip install fastacat
After this, simply use the command fastacat.
fastacat PATH
PATH is the name of the tabular file (TSV file) which needs to be
concatenated. fastacat will put the resulting TSV file, as well as a
FASTA-formatted file, in a directory called output/. The TSV and
FASTA files will be named output.tsv and output.fasta,
respectively.