The people at Visme have designed a simple infographic with eight tips to recover from a memory lapse when delivering a presentation. They expand on these points in a blog post that you can read here.
I like the tips, particularly No. 7 (don’t memorize your talk but rather know the points you want to cover so you can keep moving forward) and No. 8 (don’t try to be perfect). I would also add a couple of caveats.
Tip No. 1 is to say something … anything. However, before filling the vacuum with your voice, I would advise you to do something that is not on the infographic: pause! To be fair, Visme does say in its blog post that by maintaining eye contact (Tip No. 3) it will look like you are pausing. Many times, a pause of a few seconds will be sufficient to jump start your thought process. It has worked for me on several occasions. For more on pauses, see this post.
Tip No. 6 says to have your notes handy and scan them “surreptitiously”. My first comment is that your notes should just be the key points of your talk and they should be easy to read. My second point is that there is no reason to look at them surreptitiously. If you are really stuck, just take a moment, check what comes next and then get back to speaking. After all, nobody’s perfect (Tip No. 8). For more on using notes, see this post.