Some tips for people into memory play with hypnosis:
First off, if you're the subject, MAKE SURE that you trust your hypnotist. This is something you only wanna do with someone that you know would not abuse it. Not everyone is affected enough to where its easy to do such a thing, but that's not a gamble you want to take if you find your hypnotist even slightly iffy.
If you're a hypnotist, be sure to inform your subject of all of this and take things very slowly at first. Make sure that they want to continue before doing more. Part of hypnosis a lot of the time is some aspect of role play, but you need to discuss what each party wants and is okay with beforehand. Install safeties to make sure that if something is happening that the subject doesn't vibe with, that your suggestions can be rejected easily.
That all being said, from what I've found, you cannot make someone forget information they've already taken in. Our brains are quite stubborn in that regard. That being said, there are ways to both limit information coming in and also ways to deal with recalling information.
Suggest as a trance begins to direct the subjects focus on your words, focusing so much on each new word that it's hard to remember what was said just a bit ago, going right to their subconscious instead of their conscious memory.
Focus on redirecting their memory when attempting to recall something specific. My hypnotist introduced me to this one, where any time you try to recall what happens during trance, the thought redirects to whatever the hypnotist wants. A trigger is the simplest, perhaps something that clears their thoughts like a bubble pop or something similar. In my opinion, it's important that what their thought is directed to is something specific like a visual for it to be effective, instead of something abstract like "you will drop when you try to think."
Another option is to suggest that the subject doesn't want to recall or think about the trance. This is most effective if a lot of your suggestions focus strongly on obedience and devotion. Your subject willingly wanting not to do it can't hurt.
The last option I have seen used well is to suggest that whenever you specifically ask your subject if they can remember something, it suddenly becomes impossible to think about or remember whatever you said. It can be a nice way to demonstrate the power of your suggestion and make it feel more legitimate and possible, which will then make it more effective.
However, the most effective practice, and the thing that will really set you over the top, is combining multiple if not all of these. If you have like 5 traps set in place, even if some fail, each layer has a chance to intercept the recall.
Those are all of my thoughts, there is almost certainly more though. Happy hypnotizing!