Tiled- why does it say it cant find my files

[Lizzie2324]

I want to start by saying this is the first mod I've made and I'm fairly new to tiled and the other tools I'm using, so this may be really easy to fix and I'm just not seeing it. I'm trying to make a simple map of a field in stardew. whenever I save my map it says it couldn't find the texture files I'm using, I've been trying for a day or so and I can't find an answer so any help is appreciated.