The plate umpire may correct a wrong ball/strike count as long as the batter has not completed her turn at bat. There are other situations for which the count may or may not be changed. The NCAA 2022 and 2023 Softball Case Book has rulings for some of these.

Batter is still up

Play: The batter has a 3-1 count and although the next pitch is called a ball, no one acknowledges the base on balls. The next pitch is a foul ball. Before the seventh pitch, the offensive coach asks the plate umpire for the count and it is confirmed to be 4-2.
Ruling: As long as the batter has not completed their turn at bat, the umpire may correct the count. In this case, the batter would be awarded first base because the rules say when a batter receives a fourth ball, they are awarded first base without liability to be put out.

Play: The batter has a 3-1 count and although the next pitch is called a ball, no one acknowledges the base on balls. The next pitch is a foul ball. During the discussion about the correct count, it is discovered that earlier in the at-bat the batter took a full swing but the plate umpire called the pitch a ball. Can the umpire change one of the balls to a strike and rule the batter out on strikes?
Ruling: If there is a checked swing or full swing that is not ruled a strike, that must be appealed prior to the next pitch (legal or illegal). Once a pitch has been thrown, the call cannot be changed.

Play: The batter leaves the batter’s box headed for the dugout thinking they struck out (but has not) or heads to first base thinking they walked (but has not).
Ruling: The umpire shall direct the batter to return to the batter’s box to complete her turn at-bat. Although this play does not involve the umpire changing the count, it is an example of the duties the umpire has to ensure the count is correct.

Batter has completed her turn at-bat

Play: The batter has a 3-1 count and although the next pitch is called a ball, no one acknowledges the base on balls. The next pitch is a foul ball. Following the foul ball, the seventh pitch is a called a strike for strike three. The offensive coach immediately requests the plate umpire award the batter the base on balls they had previously earned, thus negating the strike out.
Ruling: The window of opportunity to correct the count no longer exists because the batter completed their turn at-bat. The result of the play remains the action from the last delivered pitch – strikeout.

Play: The batter has a 3-1 count and although the next pitch is called a ball, no one acknowledges the base on balls. The next pitch is a foul ball. On the following pitch after this foul ball, the batter hits an out-of-the-park home run and the defensive coach immediately requests the plate umpire award the batter the base on balls they had previously earned, thus negating the home run.
Ruling: The window of opportunity to correct the count no longer exists because the batter completed their turn at-bat. The result of the play remains the action from the last delivered pitch – home run. Note: Rule 7.3.5 does not apply as this is not a case of a delayed call or a reversed decision putting a player in undue jeopardy.

For a discussion on giving the count, see the article in the Mechanics Corner/Plate/Pitches section – Giving the Count.