By adding a negative database override to /etc/tklbam/overrides:

# exclude drupal7 database
echo -mysql:drupal7 >> /etc/tklbam/overrides

# exclude sessions table in drupal8 database
echo -mysql:drupal8/sessions >> /etc/tklbam/overrides

Or on the command line:

tklbam-backup -- -mysql:drupal6/page_cache

By default ALL databases are backed up so adding a negative database override excludes only that database or table from the backup.

Excluding a table only excludes its data. The schema is still backed up as long as the database is included.

Specifying a positive database override changes the default behavior so that only the database or table specified in the override is included in the backup.

You can mix positive overrides with negative overrides.