The reason why you cannot correct the mark is likely because this mark has been marked as “invalid”. Indeed the correction process entitles you to correct or modify any information that was included in the original submission of such trademark record to the Clearinghouse for the first time after the verification agent has completed the verification services on the trademark record. The correction process is however limited to one correction attempt per trademark record submission. If you fail to use this chance to correct your trademark record, the trademark record is then on invalid. If your record has been set to invalid but you still want to have this trademark record included in the Clearinghouse, you can always submit a new trademark record and pay again the related fees.
Your trademark could also still be under validation. This is indicated by the status “new”. In this case you will have to wait until the end of the verification process. The mark can then receive the status (1) verified which means that no further action will be requested from you (unless the proof of use is on incorrect), (2) incorrect which means that you will then be able to correct it and (3) invalid which means that you have already used your chance to correct it and are no longer able to correct it.