Anyone know the best way to update existing Inventory adjustment record to update the expiration date field ?

I would be updating the inventory number record directly via the UI. If you have a lot of inventory number records to change the expiration date on, you could do it via CSV import onto the inventory adjustment (only really worth it if you have a lot of adjustment lines to do) you can only ADD an expiration date on the inventory adjustment, you cannot change it if the expiration date for that inventory number record has ever been set in the past. If the expiration date for the inventory number is already set, the only way to change it is to edit the inventory number record directly