Use Query to Filter Table

I have a form bound to a table of available tests for a summer Credit By Exam
Session. I created a query that finds only the tests that were signed up for
by students.

I need to update information on each test for the day the test is given and
what session the test is in. I tried just linking the TestID from the Table
and the TestNum (they are the same) from the query to limit the records
available on the form. However, the form is no longer updateable.

How can I use the query to limit the table information on the form so that
only the tests that are signed up for appear? There are 157 available tests,
but only about 25-30 tests are signed up for. I don't want to update all 157
if I don't have to.
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Thanks As Always
Rip