To be able to do a pelvic floor contraction, you may need to train your brain and body into understanding what it should feel like.
Here are a bunch of tips that physiotherapists when trying to share images of what it should feel like:
Squeeze your pelvic floor as if you were stopping the flow of urine
Squeeze as if you were holding a gas
Squeeze as if you were sucking up liquid through your vagina with a straw
Imagine you are tightening your vagina around a tampon
Imagine you're retaining a grape in your vagina
Remember to keep everything else, especially your butt, stomach, and thighs relaxed. To monitor this, you can place a hand on your stomach.