Minimally you need
$config['influxdb']['enable'] = true;
$config['influxdb']['transport'] = 'http'; # Default, other options: https, udp
$config['influxdb']['host'] = 'ip or fqdn';
$config['influxdb']['port'] = '8086';
$config['influxdb']['db'] = 'librenms';
You can test to see if you can post to the database using curl using some test data like the below template
curl -XPOST 'http://your.influddb.fqdn:8086/write?db=librenms' --data-binary "somemeasurement count=1'