ض is articulated with the side of the tongue against the opposing upper molars. Many find the left side easier, though correct production may also involve the right or both sides.
In ضَالِّينَ, dad must not simply be replaced with د or ظ. Its defining articulation involves the tongue's side and the upper molar region rather than only the tip used for dal.
This letter needs careful guided practice. Scholars have discussed details of its performance; a skilled teacher’s ear is important when correcting it.