if you are on the normal JEM 2.3.2
you first make a backup.
It would be better to do it as template override. See Infos to create that.
you can go in ftp to
there is a <table class="eventtable"...
you have to move 3 parts in 3 places:
one in the <colgroup>
one in the <thead>
one in the <tbody>
PHP 7.2.9 on different sites
JEM 2.3.0dev 2.0M and specials with Joomla! 3.9.3 stable on livesites
ja_simply, ja_purity_iii, multilingual DE EN IT FR