Help with delayed tax declaration

Hiiii, So last year from December 2023-April 2024 I was working in Brussels, I moved back home after that. Now today my former roommates send me this letter that arrived in my name and I am not quite sure how to proceed since I have already given up my belgian id to the commune when I left so I don’t have a way to register to this website that they mention. Has anyone had a similar situation before?