Yellow mark on front tooth. what can be done?

Depends: Hard to answer without seeing. Sometimes tooth whitening may reduce the contrast and be sufficient. Sometimes "microabrasion" can eliminate the spot. If it is deeper, "bonding" may be all that is needed to eliminate the appearance of that spot. A good cosmetic dentist is bound to have suggestions and be able to carry out the treatment.

Yellow mark: The yellow mark that you see may be stain, or decay and it is impossible to tell you how to treat this without seeing your tooth. Your dentist can give you treatment options

Yellow mark ?: Yellow mark may be stain, discolored filling, poorly matched filling, intrinsic stain or developmental defect, etc. Your own dentist can tell you exactly what is is and how best to remove if necessary or preferred.