Well Sorry For The Late Reply
Better To Use A Child Theme but if in stock theme open sidebar.php and then change the below code:
<p><?php _e('Follow:','hueman'); ?></p>
<?php alx_social_links() ; ?>
to
`<?php wp_dropdown_categories( $args ); ?>
<?php $args = array(
‘show_option_all’ => ”,
‘show_option_none’ => ”,
‘orderby’ => ‘ID’,
‘order’ => ‘ASC’,
‘show_count’ => 0,
‘hide_empty’ => 1,
‘child_of’ => 0,
‘exclude’ => ”,
‘echo’ => 1,
‘selected’ => 0,
‘hierarchical’ => 0,
‘name’ => ‘Cat’,
‘id’ => ”,
‘class’ => ‘postform’,
‘depth’ => 0,
‘tab_index’ => 0,
‘taxonomy’ => ‘category’,
‘hide_if_empty’ => false,
); ?>`
This Will Give You A Category Selector But it Wont Be Like The Widget. I Am Trying To Make it like the Widget but till then use the above and fyi i am not that good in php,html or css