Rust at the Seat Ibiza 6J (Bj 2009) Schweller and fender

Hello guys, my Seat Ibiza 6J (built in 2009) rusts at the fender and sill. Soon there’s also TÜV. What should I do? — just check it out or more? How can I solve the problem in the long term and what makes financial sense? I am grateful for every tip. Best regards Seatfahrer123