These tutorials are aimed at improving finger strength & dexterity.

This one is aimed at getting all fingers going.  You can use all the exercises, or you can modify it to just focus the idea on your ring finger.

Trills Drills

https://www.guitartricks.com/tutorial/1829/

This one is meant to target the pinky, but it also has a lot of benefits for the middle & ring fingers because it requires using them in ways you don't normally, while still making music.

Building Pinky Strength & Dexterity

https://www.guitartricks.com/tutorial/1292/

Best of success with it!