I tapped on three-dot it did not work (step 2 above). so how can I set SD card as default on J5 galaxy mobile

[hafezeh]

I opened the setting folder. then sopened storage folder. I saw SD card. I selected it (the colour changes) but when I tap on the three-dot menue on top left SD card is deselected.

 

[Saga Lout]

In the Marshmallow flavour of Android which I believe you have, you have to go into Settings and nominate whether you want to treat the SdCard as Internal or Portable.

If you choose Portable you can't install Apps on it because they won't work if you remove the card.