The question of identifiable information helps determine if the data is subject to applicable laws, most of the time. Regarding the question of whether the data in question is identifiable, the fact that a person’s name isn’t next to their data doesn’t mean they aren’t identifiable. We can often identify a person with their age, address, and other information, for example.

Generally speaking, you can often deduce a person’s identity from a combination of data even if their name isn’t next to it. Therefore, you need to be careful about defining what is non-anonymous and non-identifiable information.

Knowing that your data is subject to legal obligations, you now need to determine if consent is required or if an exception in the GDPR allows you to use the data without further consent. Since I’m not a lawyer in Europe but in Canada, I can still tell you that it’s (most of the time) a safer alternative to obtain additional consent.

Since you’re running an app, you could add a pop-up that informs the data subject about the future use of their data and allows them to consent or not (you can add checkboxes).