TÜV criticizes rust on the threshold

Hello my dad was at the Tüv today and this has front left + right and back left + right rust faulted so quasi where the photos are to be picked up, that these completely marode or deleter are to be seen now could not give me a picture of it myself, but how is such a thing repaired ? there are complete repair plates or is it enough if you cut yourself the matching sheets and this newly welded ? am now not a body builder, but can with nem welding device around has any of you ever done such a thing ? would hate to have to weld complete repairblehce which are ellenlang would look forward to answers lg daniel