The Inventory Shrinkage account in QBO is already a COGS type of account, so it will show up as a reduction or increase of COGS.  You may want to Make the Inventory Shrinkage account a sub-account of the major COGS account.  That way you will have an overall total of the two in the top level account but can see exactly what was posted to Inventory Shrinkage.

The other thing you can do, which i think is most common, is to create an expense account for Inventory Adjustments, which will show up in the expense section of the P & L.  That is usually where adjustment numbers go.  If for any reason you want to keep it all in COGS, then follow the first paragraph.

Personally, I don't like the name 'Inventory Shrinkage' for an account.  It almost implies that the inventory shrunk of it's own accord.  Whether you decide to keep the adjusting account in COGS or expense, I might suggest renaming it to Inventory Adjustment rather Shrinkage.  I know, it's semantics.  I'm just picky that way :)