Here’s what to do:
This process requires at leastAndroid 6.
If your phone does support this option, you’ll see it in thestorage manager.
Insert an SD cardinto your gadget.

Jeremy Laukkonen / Lifewire
Your phone may have a micro SD card slot or micro SD card tray.
The tray may be shared with both the SIM and the SD card.
Go toSettings>Storage.

Tap yourSD cardfrom thePortable Storagesection.
Select thethree-dot menuin the upper right corner.
When an SD card isformatted, its contents are erased.

Back up whatever you want to keep before completing this step.
Your SD card will now function as internal storage.
Why Use an SD Card as Internal Android Storage?

The issue with using an SD card as internal storage is that they’re typically slower than built-in storage.
That isnt always the case, but it typically is.
Saving and loading photos, videos, and other files on slow cards can also take noticeably longer.
Why Cant I Set My SD Card as Internal Android Storage?
So rather than allowing you to have a poor experience, they shut down the feature altogether.
FAQ
To access your SD card on Android, go to theFilesapp.
Scroll down to theAll storagesection to see your options.
To recover deleted photos from an SD card, use an app likeDiskDigger.
Recovering files with DiskDigger requires root access to your smartphone or tablet.
Tomove files to an SD card on Android, go to theFilesapp and locate the file.
Long press the file to select it, tapthree dots>Move to, and then opt for destination.