If you ever go into an audition where a specific skill is required, just tell the casting director you can do it. Horse Riding? Yep. Gymnastics? Yep. Tap dancing? Of course. The audition process is a harsh one, and no actress wants to count herself out for a great role just because she’s not a “strong swimmer.”
I recently went for an audition in which I had to be the the 3rd best junior tennis champion in the world. I went in, I told the casting director I’d been playing tennis since birth, and I nailed my audition (I have never stepped foot on a tennis court, just FYI). I did well enough that I got a callback to meet with the director and producers later in the week. I prepared by googling a few videos of Serena Williams smashing balls across the court, and felt ready and confident to sail smoothly through my second audition.
Towards the end of the callback, after again talking up my tennis skills, the producers seemed pleased and informed me that the next phase of auditioning would take place on an actual court, with actual tennis balls, and an actual tennis coach testing my skills.
I didn’t book the job.