Format this external hard drive?
In fact, from my understanding, no matter whether you’ve formatted this drive, without replacing these original drive data with anything else, you do have chances to get all stuffs inside back with right data recovery software.
So, in your case, save no more stuffs on this external hard drive and search a right data recovery program for your inaccessible drive data.
Know more information of drive data recovery here:
No matter what happens in the future, prepare drive data backups on different places all the time.