I recommend the following:
1- When you start your Salat, take your right index finger and push it against your left thigh and say:
بِسْمِ اللَّهِ وَ بِاللَّهِ ، تَوَكَّلْتُ عَلَى اللَّهِ ، أَعُوذُ بِاللَّهِ السَّمِيعِ الْعَلِيمِ مِنَ الشَّيْطَانِ الرَّجِيمِ
2- Observe some of these tips that we discuss about concentration in prayer:
https://youtu.be/IEmVEZ-bUW4
https://youtu.be/cfYJ72ShjTc