Please help me with my External Portable hard drive

I have been using my laptop for a couple of years and so I decided to buy my own external hard drive so that I can save my files there and save some space in my laptop. However, just recently I bought a new PC. I have important files in my external portable hard drive which I want to use in my PC.
When I plugged my external hard drive to my PC, it was asking me to reformat it. I was just scared that it might have been destroyed so I didn't reformat it and tried to use it in my laptop.
Luckily, when I plugged my portable hard drive to my laptop it was working well.
What should I do so that I can also use my portable hard drive to my PC?
