If your droplet was created with ssh keys for authentication instead of a password you will not be able to reset the password. I would recommend opening a support ticket. As a last resort, they can reboot your droplet into a recovery mode which will let you reset the root password from the console and regain access. This will cause some downtime while the droplet is in the recovery environment.

I would recommend checking your droplet dashboard click your droplet in account then go to access should look something like this,
https://gyazo.com/0ff26bf1c7a2409a3943aa962423a555

If you did that and it still doesn’t work I would recommend doing what @ryanpq recommended!