photoshop bruv! it's super easy, there's a tool that lets you select all the areas with a single colour, you just swap out the background for something complementary.
you can figure out what colours might work nicely with colour palette generators online. usually, matching the temperature (warm vs cool) of the colour results in cozier vibes. but experiment!
photoshop's been cracked to hell, you should be able to find a version for your OS if you're interested in trying.