Put the SD card on your Android phone and wait for it to get detected.
Now, open Settings.
Scroll down and go to the Storage section.
Tap the name of your SD card.
Tap the three vertical dots on the top right corner of the screen.
Tap Storage Settings.
Choose format as internal option.
On next screen, you have the final chance to decide whether you want to change your mind. Tap Erase & Format if you want to format your SD card as internal storage.
You will be notified if Android finds that your SD card is slow. Tap OK to continue.
You can start the data migration process now or do it a later stage.
Tap Done to finish storage adoption process for your SD card.
After the format process completes, you have the freedom to use your removable SD card as a ‘somewhat’ permanent storage. But keep in mind, it’s not hot swappable like the portable SD cards. So, don’t remove it without using the Eject option. Moreover, you can practically remove the adopted storage but it is not recommended as it may cause errors on the device.