TOEFL iBT: The students can apply directly to ETS (http://www.ets.org/toefl/ibt/scores/cancel/) for objection to scores. First, they are required to fill in a form, which they can download from the ETS website. For rescoring of each section, the students have to pay some amount of money, which is announced on the ETS website. After depositing the required fee, the students mail the form and the bank check to ETS.
PTE Academic: The students can apply directly to Pearson for objection to scores (https://www.pearsonpte.com/help-center/scoring).