Hi SharonP,
With the +New button of the sub-grid, we can create records directly and add them to the sub-grid.
However, by default, the +New button of a sub-grid will only appear in the 1:N sub-grid.
So we need to customize the command of the +New button of the sub-grid to make it appear in the N:N sub-grid.
Create a solution and add the entity of the sub-grid in it, then open the solution in the ribbon workbench.
In the ribbon workbench, customize command of Add New {0} button.

Add new display rule, add OrRule, then add RelationshiptTypeRule in its two steps, one is OneToMany, the other is ManyToMany.


Remove Mscrm.ShowForOneToManyGrids from Mscrm.AddNewRecordFromSubGridStandard commands.

Publish.
Then we can see +New button of the sub-grid, and we do not need to search for the new record, the new record will appear in the sub-grid automatically.
