how to change a mesh and upload it?

hi!! i'm an aspiring cc creator and i'm learning the basics right now.
well, trying to.
i want to make a poster in s4s, the problem is that the objects provided are not the correct size. in blender, i edited the Z value so it's shorter and more of a square. i saved the (i think) edited version of the original mesh and tried to upload it to replace the original mesh. i was met with this error message:
"The Sims 4 Studio - Version 3.1.6.3

System.AggregateException: One or more errors occurred. ---> System.IO.FileNotFoundException: Could not find file 'C:\ProgramData\S4Studio\Scripts\f6ab3782-8708-440d-9c71-8f6a07065a65\s4s.out.mlod'.

at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)

at System.IO.FileStream.Init(String path, FileMode mode, FileAccess access, Int32 rights, Boolean useRights, FileShare share, Int32 bufferSize, FileOptions options, SECURITY_ATTRIBUTES secAttrs, String msgPath, Boolean bFromProxy, Boolean useLongPath, Boolean checkHost)

at System.IO.FileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share)

at S4Studio.ViewModels.ObjectLodItem.ImportMesh(BlenderUtilities blender_util, String blender_path)

at S4Studio.ViewModels.ObjectLodItem.<>c__DisplayClass49_0.<ImportMesh>b__0()

at System.Threading.Tasks.Task.InnerInvoke()

at System.Threading.Tasks.Task.Execute()

--- End of inner exception stack trace ---

---> (Inner Exception #0) System.IO.FileNotFoundException: Could not find file 'C:\ProgramData\S4Studio\Scripts\f6ab3782-8708-440d-9c71-8f6a07065a65\s4s.out.mlod'.

File name: 'C:\ProgramData\S4Studio\Scripts\f6ab3782-8708-440d-9c71-8f6a07065a65\s4s.out.mlod'

at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)

at System.IO.FileStream.Init(String path, FileMode mode, FileAccess access, Int32 rights, Boolean useRights, FileShare share, Int32 bufferSize, FileOptions options, SECURITY_ATTRIBUTES secAttrs, String msgPath, Boolean bFromProxy, Boolean useLongPath, Boolean checkHost)

at System.IO.FileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share)

at S4Studio.ViewModels.ObjectLodItem.ImportMesh(BlenderUtilities blender_util, String blender_path)

at S4Studio.ViewModels.ObjectLodItem.<>c__DisplayClass49_0.<ImportMesh>b__0()

at System.Threading.Tasks.Task.InnerInvoke()

at System.Threading.Tasks.Task.Execute()<--- "
did i even edit the mesh? trying to learn everything is so confusing and overwhelming, i have two different blender installations, when i copy the videos i can't even select the end of the cube and move it, i just want to give up. i can't even follow the tutorials.