You need to indicate information regarding “disposition” in you Form I-131, Application for Travel Document, only in case USCIS has ever issued you a re-entry permit or a refugee travel document previously.
You will not receive a new travel document unless you explain what happened to the one granted to you previously, especially if according to the USCIS records you already have a valid travel document. That is why it is required to provide explanation of how exactly the previously issued travel document was dispositioned, namely whether it was lost, stolen, destroyed, mutilated, returned to USCIS, etc. Fill in item 4c “Disposition (attached, lost, etc.)” of Part 3 “Processing Information”.
If your previous travel document has expired, simply insert “expired” in the corresponding field of your new Form I-131.
If you possess a valid travel document, you have to return it to USCIS putting it in the same envelope as your new Form I-131.
And if your travel document was mutilated or stolen, you may additionally provide a proof, for example, a photocopy of the damaged document or a police report confirming the theft.