I literally have exercises on my YouTube channel that I devised for the pinky specifically. There is one that starts at the beginning at the original hail to the king intro tutorial. And then there is another 1 that says finger exercises or something to that degree. A lot of people have wrote me telling me that it’s helped them tremendously! Hopefully it might help you
Honestly, the best way to train your pinky in any way is to actually use it. Like if you have 2 frets in between 2 notes use your pointing finger and your pinky.
You won’t train your pinky unless you use it!
Check out Syn’s Etudes Sweep Picking One and Legato 1, they will be a real workout and your forearm may be sore, don’t push it and injure yourself! I thought I had pretty decent pinky strength and they whipped my ass into shape real fast!