Generating an expiry date based on fields in different tables
You can create a view using a JOIN statement to combine the results of two related tables. In your design, the CourseID field appears on both the tbl_courses and tbl_training tables, using this field to perform the join you can easily derive the value that you require:

CREATE VIEW [CourseDetails] 
(
    [CourseName], 
    [CourseDescription], 
    [DateCompleted], 
    [ExpiryDate]
)
AS
SELECT tbl_Courses.[CourseName]
     , tbl_Courses.[CourseDescription]
     , tbl_Training.[DateCompleted]
     , DATEADD("d", tbl_Training.[DaysToExpire], tbl_Courses.[DateCompleted]) [ExpiryDate]
  FROM tbl_Courses 
 INNER JOIN tbl_Training 
    ON tbl_Courses.[CourseID] = tbl_Training.[CourseID];



There is a full tutorial on how to perform this that you might find helpful.