Change task start time without changing task end time

I am brand new to this, but I only seem to be able to change the end time of task, and if I change the start time of a task it just moves the end time by the amount that I change the start time. Essentially it allows me to drag a set amount of time for a task, but not to trim off from the beginning. What am I doing wrong?

if you drag the default will be to adjust the due time only leaving the defer date as it was no matter what date you drag the task to.
If you use the command key as you drag a different result is obtained. You can automatically shift the defer date at the same time.
See the Help Shortcuts

Thanks for the quick reply. I may be wording this incorrectly, but holding command does not seem to be having the result I’m looking for. I have realized that what I want to do is change the effort when I drag a task, rather than moving a set amount of effort on the timeline. Do you know if there is a way to do this? I’ll take a look at the Help Shortcuts.

Due to the many different ways a project can be setup in OmniPlan it’s often easiest to answer these types of questions if we can take a look at the file you’re working with. If you’re willing to share that, you can email us and we’ll be happy to take a look at what’s going on.

In case it helps, the online documentation contains a pretty nice tutorial that will give you quick orientation on how OmniPlan handles task scheduling.