Student or Learner
Something has come up or something came up??
Our meeting is currently scheduled for Februrary 1. Something has come up and I am no longer available on February 1. Could we change the meeting to February 5.
Because it relates to your current unavailability, use the present perfect.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.