Is it possible to build graph from the keys already stored in redis key/value storage?

Quick example:
I have redis instance with data populated in RedisJson format eg:
a lot of keys which start in bikes:… and riders:… and relations:…*
Is it possible somehow easily build RedisGraph out of data which is already in redis?
And have some auto synchronisation? In case data will be updated and to keep graph synchronised with it?

There is no built-in mechanism for this.
You’ll need to write some script to do the conversion.
As for synchronization - you can consider adding some flag to each item, indicating that you need to synchronize it, or alternatively, store it in another data structure for items waiting to be synchronized.