Welcome to the forum!
Two ways. You can get the Transit to build a Speedfusion tunnel to a free Fusionhub virtual appliance you host in the cloud (costs $5/month) video here https://www.youtube.com/watch?v=ZxZBWloVizM
Or you could setup your raspberry PI to run something like Zerotier. Accessing your Raspberry Pi securely from the Internet using ZeroTier - Kelvin Zhang