when you hae already assigned baseline to schedule, updated it for few days. Then later there is a change in the original plan, addition or modification followe the below steps.
In your current project
go to maintain baseline.
Restore it.
Close the project.
Come to home screen. You will see to 2 projects. One is basline BL1 and one is actual.
Cntrl select both, Open both.
Make the desired changes in both parallely.
Close them.
Open Actual project. Say assign basline. done use the first option save current as basline. Use second option.
Select the BL1 of the same project.
problem solved.
***i recommend not to touch any activities which have already been started (activities with actual)