how to asign multiple activities to a wbs?

Select the activities (Ctrl+Activity).

Move the cursor to the left side of the activity table. Cursor with small rectangle appears.

Now drag the activities to the needed WBS.

add a column for wbs do the first one then do a fill down 

I was looking for the solution of the same issue since last one week but in vain.... Thanks Chandran , this tip really worked...

2 options

option #1

if you can get your activities lined up or group another way then you can add a column for the wbs and then do the 1st one and then do a fill down

option #2

you can export the activites to excel when you export them if they have not been assigned they wil automatically  take the wbs of the project id that is the highest level. You can then change them in excel and import them back into p6