Note: IF you don´t see the red sign you need to contact the gym/club and ask them for advice. 

In app:

Go to your account and click Subscriptions

Find the subscription you want to cancel

There you can click Cancel subscription

Then this pops up and you click Yes

In web:

If you want to cancel a recurring subscription you go to the shop, https://www.sportabler.com/shop/ and click on Registrations.

Find the subscription and click on See more 

Then the subscription opens up, there you can click on Cancel subscription

This window will open and then you click on Confirm.