Manipulating dreams means manipulating the sub-consciousness of the target itself. You can use it to reprogram the victim itself.
I chose to make a servitor for various reasons. First of all, if you'd want to do it astrally, you'd have to know when the target is going to sleep. And you'd have to wait until the target has it's dreaming phases. It is more convenient to have a servitor do it than wait for the right time yourself.
Make a statement of intent for the core of the servitor like "To manipulate the dreams of X". Also make a mantra of that statement.
Perform an opening rite as you wish and do an energizing rite.
For example visualise a pillar of light shining down on you. Feel your aura expanding, full of energy. Imagine you glowing in the same light as the pillar.
Declaration of the SOI:
"It's my will to create a servitor to change the dreams of X S/he shall dream of <whatever> <time period - eg every night/week etc>"
Creation of the servitor:
Visualise a cord of energy extruding your solar plexus that thickens about half a meter in front of you. Shape it into a form you want it to have.
When you've done that, start visualising the core sigil in the servitors heart and chant the prepared mantra.
Now continue programming the servitor. Bind it to the target and describe the dreams the victim shall have. Also tell it how often the target should get that dream.
Finally shoot it off toward the target.
Banishing and closing rite