Solved, don't click in question was : inserting stl files

I lost all my bridging progress for a school project I was working on . I constantly pressed the save button, as it seemingly didn’t do anything, I went for the save as button, still, there was no response. I am a very careful person, still, I made a grave mistake, I accidentally pressed the upgrade to pro button, leading me to the store, which sent all my progress to hell.i was praying when I pressed the go back to the last page arrow button, obviously it didn’t work, all my progress gone. luckily , I downloaded a STL file before the accident and I thought I could import it back. apparently I need pro to import STL files. what should I do? any plugins I can use? I am just a grade 8 student and I need help.[practice HW 1.stl (289.2 KB)
Also, I think its because SketchUp wants people to buy the pro version, so it time by time create ‘accidents’ to stress out free users, forcing them to buy pro. somebody help please. I’m kinda desperate and devastated

I n e e d s o m e h e l p A S A P m y h o m e w o r k d u e s s o o n .

Use the Folder Icon top left of the screen to, Insert .stl from your computer.

that was awkward… I saw that it said upgrade to insert the followings and in it it included stl, making me think that u can’t do that on free version