I just noticed the similar topic: Created By Not Populated in App Builder.
You can indeed use the solution that @jrmi proposed. What you need to do is checking in the form what the name of your linked field to the Members table is. Let us assume that it is: Members. Next, you check what the first column (or primary key) is for this field. Assume that this is the e-mail address. Then, you can create the following URL:
http://link-to-your-form?prefill_Member=User>e-mail
This will prefill the Member field. Is this works, you can hide the field by adding &hide_Member to the url.
You can find more information about prefilling forms at How to prefill forms dynamically with existing data // Baserow.
I think the best approach is trying to prefill the form first by adjusting the URL before embedding it in the application builder.