Use any of these:
https://thedesignest.net/tanska-free-instagram-templates/
https://pixelbuddha.net/freebie/instagram-templates-free-download
https://creativetacos.com/puzzle-instagram-template/
https://www.freeject.net/2019/04/free-download-flow-gradient-instagram.html
http://graphicrefer.com/free-download-colourful-instagram-stories-psd-template/
https://mockupsforfree.com/product/black-friday-instagram-stories-template/
https://www.creativeultra.com/home/instagram-canva-stories-free-templates
https://www.graphicsegg.com/stylish-instagram-stories-pack/
https://mockupsforfree.com/product/12-shop-instagram-stories-template/
http://marinad.com.ar/free-instagram-image-sizes-dimensions-template/
Enjoy!
!