When you wish to group records for ANY query, you choose a particular field as the basis of the grouping and then in the SQL of the query, after the WHERE clause but before the semi-colon that should end all queries, include a GROUP BY basefield. If you are dealing with a combo box, the SQL is usually defined in the .RowSource property for that combo.
BUT... your question confuses me on one point and this WILL require clarification: "and then Remove the grouping" Why? Tell us in words what it is you wish to accomplish.
Having expressed concern over the form of the question, I'm now going to jump out on a limb here and GUESS that what you want might be found if you look up "cascading combo boxes" - which would be a way to refine the contents of the combo box through a SERIES of choices made one at a time. Which would have the effect of sequentiallly altering combo boxes to reduce the number of choices in the final box based on choices made for the previous boxes. AND once you "undo" the choices (perhaps by saving something and allowing the form to reset itself) then you would remove all of the groupings.