How to restore a .backup file from a single table on postgres?
I am not sure what you tried so far, please post error message for better understanding, 

Try below and post a comment if this works for you or not.

you can use pg_restore to restore a single table :

pg_restore -t my_table -d database_name database.dump

If the dump is not too big, the easiest thing to do is restore the full backup to a temporary database (gzcat backup_file.gz | psql -h host -U user database_name) dump the one table (pg_dump -t my_table), then restore it.