I started a Creo model today but just realized that I started my model sideways (BACK is actually right, BOTTOM is actually front), Is there a quick way to fix this or will I need to restart the model?
While your title states assembly, the description is about a Part.
If the problem is in Assembly, you may have to "Edit Definition" of the first component placement; assuming that the following components are referenced to the first component.
If the issue is with respect to the part; "Edit Definition" the First Feature.
IMP!!! TAKE A BACKUP OF YOUR ASSEMBLY / PART BEFORE TRYING.
I would like to explain in details if you are in part mode
if you are in part mode and your model is a simple one
then go to the sketch of the first feature
go to Sketch>Sketch setup
Now replace the plane(see the image)
After this you may face some conflict in your references
delete the failed references and add new references or replace the failed references
This is a little tricky and should be done carefully