You can change your episode publish date from the episode Settings page
If you are uploading the file from Dropbox. You can also append your publish date to the end of your filename (e.g. file_name_pd_MMDDYYYY), and will be able to pick it up as well. For example, if I want to publish my podcast, "Jack's Fun Shark Facts" on July 14, 2020, all I have to do is rename my file "Jack's Fun Shark Facts_pd_07142020"