There are different reasons one doesn't blow on Erev Rosh Hashana, one to differentiate between Elul (where the sounding is a custom) and Rosh Hashana (where it is a mitzva d'oraita), another to "confuse the Satan".
The Magen Avraham is strict according to the second reason but R Yaakov Goldstein (on OC 581:3) cites a number of sources allowing it for practice
It is forbidden to blow the Shofar, even for practice, in an open area. One is however allowed to practice blowing the Shofar in a closed
room. [This applies whether one is learning how to blow or is
trying to get used to blowing from a new Shofar. However one may
not blow the Shofar for no reason even in a closed room.]
and sources it
The Magen Avraham writes that according to the reason that this custom is
done in order to confuse the Satan, then one may not blow at all. This
implies that one may not blow even for practice and even in a closed
room. However from the Pnei Menachem and Mishna Brura it implies that even
according to this reason in a closed room it is permitted to blow for
practice.
see there for detailed references and also here