42 CFR §426.480

1. (a)Withdrawal of an appeal of an ALJ's decision. A party who filed an appeal of an ALJ's decision may withdraw the appeal before the Board issues a decision regarding the ALJ's decision.
2. (b)Process of withdrawing an appeal of an ALJ's decision. To withdraw an appeal of an ALJ's decision, the party who filed the appeal must send a written notice announcing the intent to withdraw to the Board and to any other party.
3. (c)Actions the Board must take upon receiving a notice announcing the intent to withdraw an appeal of an ALJ's decision—(1) Appeals involving one aggrieved party, or initiated by CMS or a contractor. If the Board receives a notice withdrawing an appeal of an ALJ's decision before the Board has issued its decision, the Board must issue a decision dismissing the appeal.
   1. (2)Appeals involving joint complaints. If the Board receives a notice withdrawing an appeal from an aggrieved party who is named in a joint appeal before the Board issues its decision, the Board must issue a decision dismissing only that aggrieved party from the appeal. The Board must continue its review of the ALJ's decision for the remaining aggrieved party or parties.