Use selection tool to replace the sky

With selective adjustment, you can adjust part of the image without affecting the rest of the entire image.

 1, Open the Selection panel 

 Tap the "Selection" button, and you will find a few selections Polarr automatically suggested. If you find "Sky", tap on “Sky”.

 2, Adjust the sky

 Now all the adjustments we're making here will only apply to the sky area of the photo.

 3, Add layers to the sky

 Tap on “Add Overlay” on the right hand side of the panel, and choose one of the layers you like.