First of all if you have the money get an official diagnosis. While self diagnosis is often right, ADHD symptoms can have overlap with many other things so it is better to be sure.

Now want a quick fix? If you can, get medication. It doesn't work for all people with ADHD but for those that it does it will give you the most bang for the buck.

Now there is coping strategies. Therapists can help a lot. There is also people offering ADHD coaching. This is great because the coaches tend to have ADHD themselves and understand you. It helped me personally a lot but be warned that everyone can offer coaching so quality may wary.

Last part is lifestyle. Sport. It is not optional. Running is amazing and will help you a lot but if you are not fit enough yet, walk. Walk every day for at least 30min. You need to. Also personally for me reading a physical book for at least 30min a day makes a huge, huge difference. Diet is important but what works varies from ADHD person to person. For me cutting out processed sugar was a good step.

Also no caffeine. This may also vary but completely cutting it helped me personally a lot. Yes, it helps somewhat with executive function but only in the short term and does more harm than good in the long term. Generally any form form of self medication be it alcohol, weed and so on, cut it out. Again get proper medication if you can.

Honestly accepting that you have ADHD or well at least some form of neurodivergency is already the biggest step. It gets so much easier once you learn how to properly manage it.