If the petitioner has not appeared on the day and at the hour prescribed for the joinder of the issue and has not offered a suitable excuse: 1/ the judge is to cite the petitioner again; 2/ if the petitioner does not comply with the new citation, the petitioner is presumed to have renounced the trial according to the norm of cann. 1524-1525; 3/ if the petitioner later wishes to intervene in the process, can. 1593 is to be observed.
Source: Code of Canon Law (Vatican.va)