Hi 

you can read this information detailed here ,t could help you ,       

https://www.esther-lauber.ch/index.php/en/services-real-estate-geneva/property-management/39-useful-information-on-real-estate-in-geneva/211-subletting-in-geneva-and-in-switzerland

But an advice do not try to enter thethe garage or move anything without his consent you wiill be the faulty one in this case and it is illegal to do so in Swizertland .

Good luck

Regards

I recommend to terminate the contract in writing with a prior notice of 2 weeks (by law).

After the termination, you are not supposed to prevent the tenant from using the space until you obtain a judgment of eviction. But come on, I think you should do it. 

try to contact the person to understand the reasons for not paying. if it doesn't work, you will need to enforce / collect the debt