Is it at Item Maintenance>More button upper right> Reorder?  That is where it is in our 2022 version.  I do not know if it changed in 2023. 

In our Sage 2022, I also made UDFs that display on the main pages.  One for the Bin location that reads that one, one for the backup location that we type in and one for the storage locations that we type in.   

There are people that make add-ons to Sage that are much more robust for managing bins and inventory than my UDFs, but these are enough for us.

Chris

Sage 100 Inventory Management supports a single primary bin location for each item/warehouse combination.  You will find access to set up these bin numbers as @Beevet mentioned earlier.  From Item Maintenance select your item code.  Look for the MORE Button in the upper right corner.  Use the drop down arrow to select Reorder.  On the reorder screen, you can define the primary bin per warehouse. 

If you are looking for "multi-bin", then you want to talk with your Consulting Group and the Sage 100 Reseller of Record on your account about the two options from ScanForce/DSD or Scanco; depending on the other modules you may own and use one manufacture version of multi-bin may be better suited to your business than the other.