How can I improve my REM ?

I’m consistently sleeping at least 8 hours a night. However my scores never come above 90. And one factor that’s always “reasonable” is my REM sleep.

I’m not drinking alcohol at the moment, I’m running 3 to 4 times a week and I’m playing indoor football once a week. Everyday I achieve my 10k step goal. And my diet is balanced.

I really struggle to improve my REM and I’m looking for advice on this.