“Sort everything out” is a demanding item to put on a list. It contains decisions, unknowns and several jobs disguised as one.
Try naming one action you can see yourself doing. Open the document. Put the envelope on the table. Write the question you need answered.
A smaller step can give you somewhere concrete to begin. You can decide what comes afterwards when you get there.
A question to take away: what would count as a small beginning for the thing currently taking up space in your head?