Note: Use '==' for comparison. You are setting 'pos to zero and never executing the 'if' because 0 is 'false'.
WARNING: C++ is not like Python. It doesn't care about indentation. It only cares about curly braces: { and }. From the indentation I think you might have meant:
else
{
myservo.write(90,255,true)
pos = 90;
}