Launch ON1 Photo 10 as a plugin from Adobe Photoshop Lightroom from the file > Plugin Extras menu. Once you save the image from ON1 Photo 10 it will automatically revert right back to Lightroom.
Please make sure you are looking for your edited image in your All Photographs. If you are looking under Previous Import or a Collection you will not see your edited image. To get to your All Photographs, please make sure you are in the Library module. You will see the All Photographs option on the left under Catalog:
Also, please make sure stacking is disabled. If stacking is enabled you will only see the first image in the stack and not your edited image next to the original. To unstack the images, simply right click on the stack and choose "Unstack":
If you have additional questions or problems launching the plugins from Lightroom, please visit our support page.