Today, in a space station, I accepted a new multitool from a Traveller npc, using the “get it for free and add it to your collection” button.
I found myself stuck with a crapped out 6-slot multitool and could find no way to get my maxed out 24 slot MT back.
Fortunately I had just saved and so I relogged to get it back.
How is this mechanic supposed to work anyway?
I have not tried the new multi- multi- tool, lol. I would like to know how it works as well.
I haven’t tried it but I remember reading that swapping multitools is done via the pop-up menu.
I now have 2 mutitools. I got the second one much the same way @TravelEcho describes. As far as I remember, when I was offered it, I was given choices by way of click-boxes. It worked much the same way that ships do.
I could choose to accept the new mutitool, in which case it would replace my existing one. Or I could choose to add it to my collection, in which case I got to keep both.
On PC, under the X button menu, there is now a new item that allows you to select from your collection of multitools.
Ah! Thanks muchly to you both! 
Now I’m wondering if we will be given the option to salvage/upgrade MTs like we can now do ships.
@TravelEcho: I moved your Multitool question and discussion that followed into its own topic.