Improvement/help/advice

So I taught myself the piano in 4th grade out of boredom one day and joined the band and played other instruments I've played in talent shows and church services, and other things throughout the years. Now I'm a sophomore in college and wish I was classically trained when I was younger because I've taught myself, I feel as though my fingering is kinda like just use whatever finger is closer to that key if that makes sense and I also wish that my wish were more developed and trained while I can do arepeggios and some runs I feel limited and I feel as though my playing is very stiff instead of very fluid like. Learning music is really not a problem I played the tuba and other instruments in band. I just wish I was more technically developed. Any advice on how I can improve my finger dexterity