It’s as simple as sending your complaint and/or claim through any of the channels referred to in Section 8.1.1.1 of the Terms and Conditions of Service (available here). That means you can submit your complaint and/or claim directly through the Customer Support Chat available within the YEGO App, by email to info@rideyego.com, or by post or certified fax to the registered office of the company providing the service (the address of the registered office appears in the heading of theTerms and Conditions of Service).
If your complaint and/or claim relates to an incident that occurred in Spain, you can find the official complaint form templates provided by the different Autonomous Communities: Catalonia (here), Valencian Community (here), Andalusia (here), and Aragon (here). You may use any of these templates to submit your complaint and/or claim.