If Else Statement In A Update Trigger

I am trying to build an update trigger to check the condition if checkbox is true then add 1 year, else add 3 years. The code works before i added the if checkbox = true.

Original Working code:

IF NOT UPDATE (EDITED)

UPDATE drvisit

SET nextvisit = dateadd (yy, 1, lastaudio)

FROM Apt

WHERE rec# IN (SELECT rec# FROM inserted)



Code I am trying to use with an IF Statement:

IF NOT UPDATE (EDITED)

UPDATE drvisit

IF Checkbox = True

SET nextvisit = dateadd (yy, 1, lastaudio)

FROM Apt

WHERE rec# IN (SELECT rec# FROM inserted)

Else

Set nextvisit = dateadd (yy, 3, lastaudio)

FROM Apt

WHERE rec# IN (SELECT rec# FROM inserted)