I have a memory card in my mini 3 pro drone and have taken video and photos however, my controller tells me I have nothing saved, any ideas please 

I follow a pretty similar procedure for unloading content and have been doing it in my DSLRs for years. After I transfers the images, I put the card back in the camera/drone/controller/etc and format it in the device.Just to be clear, the controller and the drone both have a place for a mini SD card. Put a card in each. You can format the card in the device. You can select where images are stored. I store them on the card in the drone and remove it each time I return home, put the SD card in the card reader and get the photos or videos and store them in the computer. Once I confirm they are transferred to the computer, I delete what was on the card and usually return the card to the drone for recording the next time. But, every once in a while I unintentionally leave the SD card in the card reader. If that happens, I take the card out of the controller and put it in the drone and I am still in business. You will get the hang of it.
Suggestion concerning "removing photos/video from card to computer and then deleting what's on the MICRO SD". I'd suggest not using the PC/laptop to delete the card data, or format the card. Just put it straight back into the drone and THEN format it through the flight app camera menu.Just to be clear, the controller and the drone both have a place for a mini SD card. Put a card in each. You can format the card in the device. You can select where images are stored. I store them on the card in the drone and remove it each time I return home, put the SD card in the card reader and get the photos or videos and store them in the computer. Once I confirm they are transferred to the computer, I delete what was on the card and usually return the card to the drone for recording the next time. But, every once in a while I unintentionally leave the SD card in the card reader. If that happens, I take the card out of the controller and put it in the drone and I am still in business. You will get the hang of it.
It makes no difference whether you format it in the computer or in the drone.Suggestion concerning "removing photos/video from card to computer and then deleting what's on the MICRO SD". I'd suggest not using the PC/laptop to delete the card data, or format the card. Just put it straight back into the drone and THEN format it through the flight app camera menu.
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