I went onto splore and was looking at another games code and I went into a game and started mucking around with the code and messed some stuff up. Did I wreck the game for the guy? I changed some sprites and stuff, I was trying to learn movement coding etc.

Other question, how to change the png. for the screen of the game in Splore and how would I go about coding a splash screen?

you only changed your local copy of the cart, no worry :]

to change the cart label, press F7 then save: https://www.lexaloffle.com/dl/docs/pico-8_manual.html#_Loading_and_Saving

to make a splash screen: what kind of help do you need?
you can draw the map or sprites or shapes as you want.
or are you asking about how to transition between states (from splash to title to menu to main game)?
or need inspiration? https://www.lexaloffle.com/bbs/?tid=2213