I thought you meant the main subform in the tab control, child 317. That's what
@MajP indicated in yellow, I think.
Click the outer border of subform Child317. As it's in a tab it might be hard to get. Sometimes you get the subform, and other times you get the tab itself. That's what you want. The actual container control for the subform. Then right-click that and select properties. That's effectively the control on the main form that represents the subform.
The data tab shows the links, and they are blank. I presume that's the subform you mean, child 317. You need a master field from the container form, and a linked field for the subform. It might be multiple fields.
You can achieve the same thing in code, by making the query for the subform actively depend on a value in the parent form, or in a variabel somewhere, and then requerying the subform in the current event of the container form.
eg, you can't link two continuous forms directly, but you can do it code, and you can do it by managing a linking field common to both subforms in a container form holding both subforms.
