Hi,
1.- Admin Dashboard:
1a.- Make sure that Settings / General / Parent categories is ticked.
1b.- Make sure that Appearance / OsclassWizards / Templates / Item Post / Category multiple selects is OFF.
2.- item-post.php, replace this block:
<div class="form-group">
<label class="control-label" for="select_1">
<?php _e('Category', OSCLASSWIZARDS_THEME_FOLDER); ?>
</label>
<div class="controls">
<?php if ( osc_count_categories() ) { ?>
<?php if(osc_get_preference('category_multiple_selects', 'osclasswizards_theme') == '1'){ ?>
<div class="cat_multiselect"><?php ItemForm::category_multiple_selects(null, null, null, osc_esc_html(__('Select a category', OSCLASSWIZARDS_THEME_FOLDER))); ?></div>
<?php }else{ ?>
<?php ItemForm::category_select(null, null, osc_esc_html(__('Select a category', OSCLASSWIZARDS_THEME_FOLDER))); ?>
<?php } ?>
<?php } ?>
</div>
</div>
with:
<input type="hidden" name="catId" id="catId" value="1" />
(If your single category doesn't have ID 1, change value here)
Regards