You should not send raw files to your printer. It is rare that they will be able to actually interpret the files the same way as the settings you generated in Lightroom. You should send them tif files or jpeg files. That is the ONLY way to ensure your images will be correctly printed. Just make sure you get the settings in the export right (use the little slider icon next to the sharesheet item to finetune the settings). If you are 100% sure they can deal with your raw files and you really really really want to do that, what you need to do is use the Export to Files option and tap on the little icon on the right that looks like two sliders. Select "dng" there - NOT original. Then tapping the folder icon on the left should export your image to an your icloud drive, dropbox, local smb fileshare, USB drive, or whatever you have connected to the files app on your phone as a raw file with all the settings embedded. Notice that ONLY Adobe apps will be able to understand the settings. All other apps will show you an undeveloped raw image.