What is the easy way to move an activity from lower level of WBS

I have received a Pre-Comm/Comm schedule from our contractor , now my management wants me to add remaining construction activities to this schedule to drive mechanical completion , So I added Sub WBS to the existing WBS. There are more than 1000 activities which needs to be moved to the next lower level. if you understood my question please advise the easy way to move activities in quick manner from one level to other level.

Thanks