Dear Mrs./Miss/Ms. Smith
I'm afraid I will not be able to visit you (albo to come and see you) this Wednesday as my trip to Gdansk has been postponed. The earliest day I can come and see you (albo visit - w pierwszym zdaniu napisz jedno a w tym drugie) is Friday. If Friday suits you, please confirm by email.
Kind regards,
Jesli wizyta ma charakter sluzbowy to nie pisz "visit you" tylko "meet with you".