Hi
This issue is a classic one that we have all dealt/deal with.
Don't be overly uptight and anxious about the issue. When the thought comes your way sort of blow it away, firmly but without facial grimaces and grosse kavanos. Soft but steady.
Fill your mind with a Torah thought- it need not be a Rabbi Akiva Eiger necessarily, any thought that you enjoy thinking about. If not bedee-eved a dvar reshus like sports
Daven for help during shmonme esrei. In the same way. Smile and say to Hashem you who are the source of all bracha please take this away. Again, no overly facial grimaces that make you look in some kind of pain.
This to me at least is crucial -I find the heavy anxious way of Tefillah and overall attitude to be only counterproductive.
Believe he will help you - you are sincerely reaching out, of course he will.
Hatzlacha!