You have to save your data by some method prior to resetting, there is no way to recover it after a reset unless you saved it somewhere. Your apps and settings get saved with your phone's backup. Your contacts and photos get backed up to Google. Anything else, documents, photos that were not saved to Google due to not having enough cloud storage, downloads, etc. need to be saved to a computer, external hard drive or flash drive. There are many apps that will automate this process for you and/or remind you to do so.
I backuped my phone yesterday through Samsung Smart Switch using a usb flash drive with an usb c adapter attached to the usb flash drive. After each security update I do an everything backup through the backup in settings.
