Everything that is on that card is gone.
Once you made the card "Internal" storage it was encoded to work with only that device. When that was done, certain things were put on the phone to make the card able to recognize it. When you reset the phone, you wiped the connection. There is no way to get it back.
You can use the card again, but you would have to format the card, which will erase everything on it. However, that won't really make a difference in your ability to get any of it, because it is not accessible by any device now (the data), so formatting at least will give you access to the SD card to use for new data.
Should you choose to format it and make it "Internal" again, or get a new SD card and do so with that, just make sure you remember you can't reset the device (not any version of a reset) without losing the data on the card, again. So, should you make it "Internal" again, you would have to back up said data somewhere else (google account, computer, etc.) so that you can gain it back should this happen again, or move all the data off the card and return it to being "External" storage prior to any new resets.
NOTE: You can save files, but you can't save apps. Also, a card doesn't have to be "Internal" storage for anything but apps, so keep that in mind.