On iPhone or iPad
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:
Start in the edit view
Tap on the square symbol (on the left of "...") on the right
Choose a preset or enter one manually
Here is a demo:
From the home screen, in the "Create" collection, you can select resize dimensions you like and upload your picture on it to edit it.