Help my sims are gone

Bix27  If you know where your save is, you'll need to move it to the Sims 4 folder the game is currently reading.  Here's how to find it:

https://sims4.crinrict.com/eng/2018/07/how-to-find-your-user-folder/

If you can't find the save, open a File Explorer window, click This PC in the left panel, and enter Slot_ in the search field in the upper-right corner.  The search will take a while to finish.  When you see the save you're looking for, and you may know it by its modified date, click it and then click the "Open file location" menu button to jump to its location.