"... you should be using use (changes that shell only), ..."

use is an option; not a requirement. Fix with: s/should be using/can also use/ (or similar).

"... not switch (changes all shells)."

That's incorrect. Fix with: s/changes all shells/changes subsequent shells/ (or similar). Below, I show starting two shells both using 5.34 — I change to 5.32 in the second shell; the first shell remains at 5.34; after that I start a third shell which uses 5.32.

$ # Shell A

$ perlbrew list
 * perl-5.34.0
   perl-5.33.5
   perl-5.32.0
   perl-5.30.0

$ # perlbrew switch in Shell B

$ perlbrew list
 * perl-5.34.0
   perl-5.33.5
   perl-5.32.0
   perl-5.30.0
[download]

$ # Shell B

$ perlbrew list
 * perl-5.34.0
   perl-5.33.5
   perl-5.32.0
   perl-5.30.0

$ perlbrew switch perl-5.32.0

$ perlbrew list
   perl-5.34.0
   perl-5.33.5
 * perl-5.32.0
   perl-5.30.0
[download]

$ # Shell C

$ perlbrew list
   perl-5.34.0
   perl-5.33.5
 * perl-5.32.0
   perl-5.30.0
[download]