How can I make hatches with relational border

Hi experts,

sometimes I have to open DWGs from outside (not created with Draftsight). If I try to edit hatches inside this drawings are no more relations between the hatch and border line so I can't edit the hatch. Also the hatch itselve has no vertices to drag. What is the best way to recreate the relation between hatch and border line without the need to delete border or hatch?

Thanks