According to the achievement code (see below), you need to control state 341 (Edirne). Usually that means you need to control all the cities with victory points in that state, and the achievement should be yours.
When I went for this back in 1.7, the achievement fired as soon as I took Istanbul. But they've re-designed the Turkish states since then, so perhaps it might not be so quick nowadays.
Either way, if you take all the provinces in that state, you should have the achievement.
Code:
once_more_mate = {
id = 27
possible = {
is_ironman = yes
difficulty > 1
has_start_date < 1936.01.02
has_any_custom_difficulty_setting = no
game_rules_allow_achievements = yes
tag = AST
}
happened = {
controls_state = 341
}
}