If you don't mind the data loss or there are no files existing on your iPhone, transferring photos to your iPhone from PC using iTunes is also a workable way.
Step 1. Connect your iPhone to your PC with a USB cable and wait for iTunes to launch automatically.
Step 2. Unlock your device and trust the computer. If required, enter your iPhone passcode to continue.
Step 3. In iTunes, click the "Device" icon in the top left corner.
Step 4. Choose "Photos" in the left panel and check "Sync Photos".
Step 5. Select the photos you want to transfer from the option "Copy photos from".
Step 6. After the selection, click "Apply" to start syncing photos from Windows 10 to iPhone. When it has done, go to the Photos app on your iOS device to check the transferred items.