You will have to use the Zapier Webhook to fetch/catch the Subscription cancellation event from PayPal. Then, you can create a simple Zap to deactivate the Client account in Trainerize.
Step-1
Step-2
Then you can apply a conditional filter to pass the data to Trainerize App module and deactivate the user.
I did some digging into this, and it seems like we have an existing feature request to support cancelled/failed subscription trigger. I have added your vote to the feature request. That does a few things:
Bring this to the attention of the integration developers
Help track interest in this feature being implemented
Allows us to notify you via email if this feature becomes available in the future
While I don't have an ETA on when this feature might be implemented, we will notify you via email if it is!
In the meantime, you can use the Webhooks By Zapier as a workaround as @growwstacks suggested.