Alright, first things first.
You text her, say something flatgering like:
"I see i have your number... Where's the like button?"
After that keep flirting set up a date,
When you're on the date be sure to DHV!
Play the Cubegame and the 5lie game!
If you DHV enough, she'll see you're diffrent from her ex!
Don't talk about the ex at all!
Don't DHV too much, you're not a dancing monkey

Be funny/cocky and make her laugh allot!
If she says stuff like: i'm actually fling in loge with my ex blablabaabooh
You should say something like:
Ah yeah i'm dating this girl, it's a really funny story so she is sitting in front of me, and she tells me she wants to go backgo her ex! Isn't that a cool story?!
Keep the enthousiasm in there!
There are some tips/rules/tricks i usually do,
Goodluck dude, the exboufriend deserves a great mental smack in the face!
EB
P.s.
(i'm not an expert, i'm just saying i would do it like this)