PHP Compatability Issues

Hello Guys

I have a compatibility problem with a custom made plugin on my site and the PHP Version.
I used the Plugin “PHP Compatibility Checker” to scan the plugins in use on my website https://www.amolep.com and I got the following Error protocol for a custom Plug in I have called “T-Shirt Country Combinations”
Here is the Error protocol I got

FILE: /home/www/web11/html/wordpress_amolep/wp-content/plugins/amolep-tshirt-combination/Tshirt_combination_form_class.php
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FOUND 13 ERRORS AFFECTING 10 LINES
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462 | ERROR | Extension ‘mysql_’ is deprecated since PHP 5.5 and removed since PHP 7.0; Use mysqli instead
466 | ERROR | Extension ‘mysql_’ is deprecated since PHP 5.5 and removed since PHP 7.0; Use mysqli instead
512 | ERROR | Extension ‘mysql_’ is deprecated since PHP 5.5 and removed since PHP 7.0; Use mysqli instead
527 | ERROR | Extension ‘mysql_’ is deprecated since PHP 5.5 and removed since PHP 7.0; Use mysqli instead
543 | ERROR | Extension ‘mysql_’ is deprecated since PHP 5.5 and removed since PHP 7.0; Use mysqli instead
543 | ERROR | Extension ‘mysql_’ is deprecated since PHP 5.5 and removed since PHP 7.0; Use mysqli instead
549 | ERROR | Extension ‘mysql_’ is deprecated since PHP 5.5 and removed since PHP 7.0; Use mysqli instead
549 | ERROR | Extension ‘mysql_’ is deprecated since PHP 5.5 and removed since PHP 7.0; Use mysqli instead
550 | ERROR | Extension ‘mysql_’ is deprecated since PHP 5.5 and removed since PHP 7.0; Use mysqli instead
558 | ERROR | Extension ‘mysql_’ is deprecated since PHP 5.5 and removed since PHP 7.0; Use mysqli instead
558 | ERROR | Extension ‘mysql_’ is deprecated since PHP 5.5 and removed since PHP 7.0; Use mysqli instead
559 | ERROR | Extension ‘mysql_’ is deprecated since PHP 5.5 and removed since PHP 7.0; Use mysqli instead
573 | ERROR | Extension ‘mysql_’ is deprecated since PHP 5.5 and removed since PHP 7.0; Use mysqli instead
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FILE: /home/www/web11/html/wordpress_amolep/wp-content/plugins/amolep-tshirt-combination/plugin-update-checker/vendor/ParsedownLegacy.php
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FOUND 1 ERROR AFFECTING 1 LINE
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1412 | ERROR | Indirect access to variables, properties and methods will be evaluated strictly in left-to-right order since PHP 7.0. Use curly braces to remove ambiguity.
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Here is the PHP Code referred to (for example, for line 462):

if (!$gaSql[‘link’] = mysql_pconnect($gaSql[‘server’], $gaSql[‘user’], $gaSql[‘password’])) {

Line 466

if (!mysql_select_db($gaSql[‘db’], $gaSql[‘link’])) {

How do i resolve these Errors?
Thanks

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