Ax1000

I use Korg AX1000 guitar and Rockwell (it's Korean made and I think that's Stratocaster, but with a humbucker bridge pick up). It sounds very good but still too "lean." I wonder if I can make sounds more "thick"? Just for an example, as its Deftones' Stephen Carpenter guitar.
I am not an experienced guitarist, so I do not know what I need material to make my guitar sound thick. I play metal and alternative.
I appreciate all the answers.

Your AX1000 should be able to get you want you want. The "start" guitar is known for its fine sound. The only suggestion would be to try different strings. Try some flat wound strings that can give you that "thick" sound you've been looking for.

If you play metal, you need distortion. Go down to your local guitar shop and try a few distortion pedals. Boss and Digitech make good not too expensive. Try a bit of reverb, which gives you subtle echoes as if you were playing in a larger room or hall. Chorus multiplies the sound of your guitar to make it sound as if there were 2, 4 8, or even to play the instrument. They all have their place, and all thicken your sound. Give them all try, but start by distortion.