If you want to create a new Performance Review Record and automatically enter the Reviewer ID number matching the Account Name, Run this script:
Go to layout ["YourReviewerLayout" (Reviewer)]
Enter Find Mode 
Set Field [Reviewer::ReviewerName ; Get (AccountName)]
Set Error Capture [on]
Perform Find 
Set Error Capture [off]
If [get (foundcount) > 0 /* a reviewer record was found */]
Set Variable [$RevID ; Value: Reviewer::ReviewerID ]
Go To Layout ["Performance Review" (Performance Review)]
Set Field [PerformanceReview::ReviewerID ; $RevID ]
Show custom dialog ["No Reviewer records with " & Get(accountname) & " was found."]
You can also create a relationship and define a lookup to do this.
Define an unstored calculation field that returns text, cAccountName : get (accountname).
Define a relationship
PerformanceReview::cAccountName = Reviewer::ReviewerName
Set an auto-enter field option on ReviewerID to lookup Reviewer_ID from the Reviewer table to automatically copy that ID number into any new record created in Performance Review.