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It's just another way of saying turn it off and start it up again but its unusual to see it in smartphones. In Android versions 6 onwards (I think) it is possible to use an SdCard for internal storage but it has to be nominated for that purpose. After doing that, it can't be reversed and it won't nominate if it has already been used for external storage.
Take the card out and use a full size SdCard carrier to slave it to a PC or laptop. Format it in FAT32 and see if that soles the problem when you put it back in.