I think I have that issue as well

Tongue chewing exercises like Mew recommended 

in the beginning it was very difficult to reach the soft palate, after some time I got (OMC) and chew for longer, after some time I saw some red "things" on my soft palate looked like blood , so I knew I had gotten there, the time was passing and these "things" were disappearing until there were no more

Two myofunctional exercises have helped me:

First exercise: Take two tiny rubber bands and place one on the tip of the tongue, and the 2nd a little farther back to where the tongue should hit the 2nd spot, then make contact to the roof of the mouth, and practice proper oral posture. This induces sensations and muscle memory. Do this for around 30 min a day. I could see it help in bridging the gap from the 1st spot to the 2nd.

Second exercise: Look in mirror and open mouth wide, cheeks back in creepy smile and mandible down as open as you can. Tip head so you can get a good look at your upper palate. As you look in the mirror, fit your tongue to the roof of your mouth, suction, fold, stuff, whatever you need to do to hit the 1st, 2nd and 3rd spots. Take a look at what needs balancing, what areas are struggling, and hold for as as long as possible. "Click" your tongue off the palate, rest, then begin again.

These are both cornerstone exercises, and the 2nd one especially helped me learn more about my tongue and proper tongue placement. First week was difficult as I adjusted my posture after the mirror work, and I kept making weird throat sounds as my tongue fell down. After that, it's been a lot easier.