Probably they mean a check of conflict of interest.Better wait for it to finish.
your employer offered you a job, you agreed and you both signed on the appt letter. Then they said they weren't sure if they could hire you? what kind of a company is that? what job is that?
why do you want them to void the appt letter and reconsider hiring you? is there something you are afraid of being found?
It is not difficult to find a job, you found it already.