Cancelling calculated planning

Hello,

I'm trying to cancel a calculated planning. We don't use automatic calculation because we don't control every ressources in project (i know, it seems to be a strange organization...).
Unfortunately, one of my project manager use the automatic calculation button and now, we have automatic plannified dates for activities and it's not possible to cancel it...

If there another solution than deleting activity and creating a new one ?

Thx

JM

That's what i do.

Thanks !

have a good day