I have not done it yet but asking the help desk . It seemed so uncommon that they didn't have a procedure for it , you simply have to send a proof of ownership to the court it seems . They gave me the advice to contact a bankruptcy lawyer . This is the answer Jack McLaughlin gave me :
" There is really no need to file a proof of interest because once the bankruptcy case is closed , the debtors still exist and still owe any debts not paid from the bankruptcy estate . If the trustee were able to pay all the debts and the company continues to operate , your equity interest would be unimpaired . If there are surviving debts , your equity interest would be subordinated to those debts and so would be valueless . "
I guess we simply have to wait till the bankruptcy case is closed .