This should do it, let me know.
var bool newPlacement = [Entrance Reason] = "New Placement";
var bool changedRoom = [Entrance Reason] = "Customer changed room";
var bool newRoom = $newPlacement or $changedRoom;
var bool customerReturned = ([Entrance Reason] = "Customer returned after preclearance departure");
var bool positiveContact = $newRoom and ([Reason for Placement]="Customer had contact with known positive");
var bool customerSymtomatic = $newRoom and ([Reason for Placement]="Customer is showing symptoms");
var bool customerPositive = $newRoom and ([Reason for Placement]="Customer is positive");
var bool noSymptoms = IsNull([Last Date COVID-19 Test Completed]);
var bool noSymptomsDate = IsNull([Date of First Symptoms]);
var date symptomsDate = If ($noSymptomsDate, ([Placement Date] + Days(10)), ([Date of First Symptoms] + Days(10)));
var bool noCovidDate = IsNull([Last Date COVID-19 Test Completed]);
var date covidDate = If ($noCovidDate, ([Placement Date] + Days(10)), ([Last Date COVID-19 Test Completed] + Days(10)));
var date fourteenDays = [Placement Date] + Days(14);
var date tenDaysAfter = [Initial Placement Date] + Days(10);
If ( $positiveContact,$fourteenDays,
$customerSymtomatic, $symptomsDate,
$noSymptomsDate, $covidDate,
$customerPositive, $symptomsDate,
$noSymptomsDate , $covidDate,
$customerReturned, $tenDaysAfter)
Neil Schneider