You might want to use your own image as background in PhotoRoom and add an object to it and edit the whole image.
Here is a trick to help you out:
From the home page:
Tap on "+" to import your background
A part of the image will disappear, it is normal
Tap on the white background option
Then, tap on "Object"/"Product/"Person"
Scroll down in the edit menu
Tap on "Cutout options"
Select the "Original" option
Your original background should be restored
Now, tap on "+Image" or "+Text" to add the images or texts you want to it
Another option would be to:
Select the white background
Tap on "Background"
Tap on "Replace"
Tap on "Photos"
Select the exact same image you have initially imported