Stuck- Can't Edit or Modify Meshes in Sims 4 Studio

I am VERY new to using Mods/CC in Sims 4... and trying to find help with my issues has been really hard!

my interest is in building/designing homes... so, I've been downloading content however I cannot recolor the items I downloaded. For example:

I downloaded this wrap-around couch from Sims Resource, but when I tried to use it in Sims 4, it didn't give me any options to recolor it. I went back to the creators page I downloaded the couch from & in the creator notes was: Recoloring Allowed: Yes - Do not include mesh

I found out I can edit the couch + colors using Sims 4 Studio. I found tutorials however, after selecting the item (I want to edit), instead of open the panel I've seen the editing tools, a window pops up asking me to save a file... I would include the screenshot of it but I don't know how to add it in here.

did I not install S4S correctly? did I not save S4S correctly on my PC? did I not put my content in the right Mod folders?

any clarification or guidance for this! thanks in advance!