You can start out by adding purposeful pauses. At the end of a point you want to really hit hard, build in to your script you literally standing there and just thinking “pause,pause,pause,pause”. Then you get more comfortable doing it and can add it in with differing lengths where needed. Eventually with work you’ll start replacing ums with pauses.
Also, purposefully slowing down can help since you likely talk too fast when nervous anyway.
Not the OP, but for me it just took a bit of mindfulness while presenting, and the realization that your pauses seem way more unbearably long to you than they do to your audience.
Not sure if there's some technique to it. I got very conscious about the ums and aahs and practiced forcing myself to stop and stay silent. I was recording short videos (1-15 minutes) about 3-5 times a week and I guess just delibrate practice helped me.
Also, purposefully slowing down can help since you likely talk too fast when nervous anyway.