Below is my successful (abbreviated) formula. I'm not familiar with how to get the User ID though. Hope this helps!
//list all installers scheduled on this date. convert to email address, then back to user
//table ID: _DBID_SCHEDULE, FID 79 = installer email, FID 6 = date
var text PullUsers= "{6.EX.'"&[Date]&"'}";
var text UserEmail= ToText(
GetFieldValues(GetRecords($PullUsers,[_DBID_SCHEDULE]),79));
var text AllUsers= $UserEmail;
var user UserOne= ToUser(Trim(Part($AllUsers,1,";")));
var user UserTwo= ToUser(Trim(Part($AllUsers,2,";")));
....
ToUserList($UserOne, $UserTwo, $UserThree,
...)
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Anne Martin
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