In order for you to manage DNS with Vultr, you will have to save your Vultr API key to your Ploi account.
Head over to my.vultr.com/settings/#settingsapi and log in. After that, press the copy button to copy your API key.
Copy this token and go to your Ploi profile to Integrations, scroll down until you see DNS providers, and enter the token there.
You will now be able to attach your sites to your Vultr DNS API key and manage DNS records. To do this, head over to your site in Ploi and press the "Settings" tab, next scroll until you see "DNS Settings" and enter the right provider, and the domain name. Now a DNS tab will show up and you'll be able to manage DNS records directly from Ploi.