(Question of the type "how do I do <x> with programming language/framework/platform <y>?" are better answered on stackoverflow.)
The https://devcenter.heroku.com/articles/proximo, https://elements.heroku.com/addons/quotaguardstatic, https://elements.heroku.com/addons/fixie are addons which provide a tunnel and static IP. They charge by requests though, making it possibly expensive (but of course people use Heroku for that kind of convenience).
If you decide to setup your own tunnel/VPN, I was recently happy with https://privatepackets.io/. They setup a digital ocean machine for a fixed $5 (and you incur the usual running costs). Now you have one more system which requires maintaining and securing.