I have created a form in model driven app but i need to insert a subgrid of the gradchild
which means there is one main form and subgrid of that and i need to add another subgrid related to the previos subgrid
how do i do that

I have created a form in model driven app but i need to insert a subgrid of the gradchild
which means there is one main form and subgrid of that and i need to add another subgrid related to the previos subgrid
how do i do that
You can achieve it by adding a nested grid in the legacy editable grid control or the new Power Apps grid control.
Here are some useful blog posts about it