The issue is that this item is serial and bin controlled but was not put into a bin when it was created (off a credit memo) but to adjust out the system is requiring a bin number. I will need to either unset the item as bin controlled or move it to a bin to export.

There are 1k plus items at different locations that we need to write-off and adjust out of our system. Is there an easy method to do this or is the methods above the only ways?

Try putting it into a Bin via a Bin Putaway transaction first.