When we are holding Service PO but it is not coming in Change Mode when we Reopen for saving Purpose

Sir

If we hold Service PO & and reopen for Change Document date. Document date filed is Appearing in display Mode, so how we can change Document date if PO Order is hold.

Note: We are Treating Message no. 06028(Purchase order date is in the past ) as per Error message. that’s why we want to change Document Date as per Date of final save.