make sure you have themes folder inside your ~/.doom.d, then run this command
wget https://raw.githubusercontent.com/Everblush/doomemacs/main/everblush-theme.el -O ~/.doom.d/themes/everblush-theme.el
then you can enable the theme in your config.el (you should know how to do it right?)
If you use straight and use-package
(use-package doom-everblush-theme
:straight (doom-everblush-theme :type git :host github :repo "Everblush/doomemacs"))