Sometimes, you want to create an image in multiple formats. For instance, you might want to list it on eBay, Poshmark, and Instagram. Or, you might want to create an Instagram Story from your Poshmark listing.
To resize your content in PhotoRoom from Edit:
Start in the edit view
Tap on the square symbol labelled "Resize" on the right
Select Resize Fill or Resize Fit
Choose a preset or enter one manually
To resize from the home screen, in the "Create" collection:
From the Create Home Screen
Scroll down to "start from a blank canvas"
Select Custom (Enter size in pixels), Landscape, Portrait or Square
Finally you can upload your picture on it to edit it
Here is a demo: