If you are sure that the application is definitely going to meet up with expectations, then there is actually nothing difficult as you can use Google advertisement.
You can join different groups on telegram about cryptocurrency investment and trading. You do the same thing on WhatsApp groups and start promoting them app by telling people how they are and help them in cryptocurrency Trading.
The social media would be the best way to market the app. If you are the owner of the platform, you should add a referral bonus on the app inorder to compensate any one who brings a new user.
The best method to use and market a trading app should be through social media platforms using links, adverts, and also referral , you can also inform your friends and family .
You need a marketing place, without a market,you can't make your app known.after that, you need to make potential customers interested in your app.engage in paid affiliate,when people can gain from something,they always try to double their efforts.use that psychology to your advantage.