Therein lies the problem. You must physically find them in the settlement (so far as I know). Is there a way to call up a list of your settlers in a given settlement, reflecting their active or inactive assigned jobs?
Havn't tried it yet, but I could have sworn there is a bell thing you can build that summons everyone. Not bothered with it yet because I can't attract folks to my settlement.
If you want to attract settlers, you build a radio mast.
If you want to check if one arrived, watch the settler number in build mode.
When you know they are 'on site', build a bell to call them.
Yes, you can craft a bell to ring and call them but it is still a messy exercise.
Settlers should have a random name, eg Dave with a subtitle underneath his name