Hard to know exactly...but the $$ in this box are supposed to be a non-taxable return of capital....that reduces your cost in whatever fund distributed the $$.
IF the $$ on the form are being displayed in the proper box, you may not have to do anything other than make sure whatever funds distributed the $$, those funds have recorded the reduced Basis in those same holdings. IF you are tracking their cost basis yourself, for confirmation, you would need to know what fund the $$ came fro
m, and see that the before/after cost basis has been changed appropriately in
whatever
records you are keeping.