If you read the instructions in the link I posted it says : If the Box 1 amount hasn't been adjusted for your housing allowance, enter a Line 21 adjustment to income
In your case it HAS been adjusted since it is NOT in box 1 ... you will NOT use the line 21 adjustment.
Follow this instead :
https://ttlc.intuit.com/questions/2303656-how-to-enter-clergy-housing-allowance
