SetPasswordSaveAction.cs

public class SetPasswordSaveAction : UserBaseAction
{
    private ID _formId;
    public override void Execute(ID formId, AdaptedResultList adaptedFields, ActionCallContext actionCallContext = null,
        params object[] data)
    {
        _formId = formId;
        var password = adaptedFields.GetEntry(PasswordField, "Password")?.Value ?? string.Empty;
        var userName = Tracker.Current?.Session.Contact.Identifiers.Identifier;
        var user = Membership.GetUser(userName);
        if (user == null) return;

        var tempPass = user.ResetPassword();
        user.ChangePassword(tempPass, password);
    }

    public override FormItem CurrentForm => FormItem.GetForm(_formId);
}