According to the cancellation rules, either of the partners can cancel the deal within the first 12 hours from the Confirmation of the Trading deal's terms without facing any penalty.
Simply write on the platform chat that you would like to cancel the deal.
If it has been over 12 hours since the date of acceptance, then a cancellation fee of 1.95% will apply to the party responsible for the cancellation. The only exemption is when the other party involved in the deal decides to waive the penalty.
Please refer to the cancellation rules here.