Pico8 carts are just a special flavor of png. I would try running it directly or if it won’t run them with the png extension just rename the file from .png -> .p8 without converting and see if that works
Relevant section of the user manual
There are three ways to share carts made in PICO-8:
1. Share the .p8 or .p8.png file directly with other PICO-8 users
Type FOLDER to open the current folder in your host operating system.
Although if you are having trouble you might have more luck getting started with the built in SPLORE command
Relevant section of the user manual
This might be easier to get started with since it will all get wired up automatically for you
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