This support article will explain how to convert old plugin templates that were created prior to the new 3Play Plugin Builder (released Summer 2018).
Step 1 - Click Settings
On the top, right-hand corner of the My Files page click Settings.
Step 2 - Click Plugin Templates
From the Settings menu click Plugin Templates located on the left-hand side of the page.
Step 3 - Check Existing Plugin Templates to Convert
There will be a Convert Template button next to any templates that are convertible.
If you are using a v1 template, you will not be able to convert the template.