Yes it's possible by using a macro or a button on a form.
You obviously need to add a new field in your table to store the new +4 week date.
For the query... to add to a date range use the DateAdd function. It's probably easier to look at the help file for this function rather than try and explain everything but here's what it will look like: DateAdd("w",4,[yourfield]).
Note: "w" might need to be "ww". Check the helpfile for exact requirement.
Now you just need to create a form and use the button wizard (if you're not familiar with VBA) to call the query.