Change Old Server URLs – critical error (v.2.9.9)

Hi there, recently my hosting server updated their server url so all of my slide images became invalid. I attempted to use the [Change All URLs] button in the Help and Support page but encountered the following errors. It did update the images URL for the 1st slide but the rest of the slides are untouched.

Can you please advise?

Fatal error: Uncaught Error: [] operator not supported for strings in /home/public_html/slsdinc.com/wp-content/plugins/ultimate-responsive-image-slider/help_and_support.php:97 Stack trace: #0 /home/public_html/slsdinc.com/wp-content/plugins/ultimate-responsive-image-slider/ultimate-responsive-image-slider.php(545): require_once() #1 /home/public_html/slsdinc.com/wp-includes/class-wp-hook.php(287): RIS_Help_and_Support_page(”) #2 /home/public_html/slsdinc.com/wp-includes/class-wp-hook.php(311): WP_Hook->apply_filters(”, Array) #3 /home/public_html/slsdinc.com/wp-includes/plugin.php(478): WP_Hook->do_action(Array) #4 /home/tomokoi2/public_html/slsdinc.com/wp-admin/admin.php(259): do_action(‘ris_gallery_pag…’) #5 /home/public_html/slsdinc.com/wp-admin/edit.php(10): require_once(‘/home/tomokoi2/…’) #6 {main} thrown in /home/public_html/slsdinc.com/wp-content/plugins/ultimate-responsive-image-slider/help_and_support.php on line 97
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