We currently do not provide a script/system that allows you to migrate from Laravel Forge, this is because it is not visible to us what has been installed on that server and what repositories have been used. It would most likely even be more unstable to migrate than to create a new server.
We recommend you create a fresh server with Ploi (Who doesn't like the fresh feeling of a new server ?), and create the sites/applications accordingly that was present on the old server.
To make the process even easier you can use their API against our API to sync up your servers and created sites.