Combine two emails?

Hey, the following happened to me… there is my normal email address (the one from Gmail) and the email address that you get from Apple (for example, when you sign up for an app through Apple).

Unfortunately, I have two accounts on Booking.com with two email addresses. I'm already at Genius Level 2 on one account, and I have a balance of €46 on the other, which means I was stupid and "served" two accounts by using different email addresses.

I only noticed this when I wanted to redeem my credit… and couldn't find it in the app. Is there a way to combine these two email addresses? Combine the progress I've made in both apps?

I imagine it would be really difficult, but maybe someone knows a lot about this and can give me a tip.

Thank you in advance 🥰