Advise on how to install pl/perl on existing DB.

psql (9.6.0, server 11.3) linux

Hi:  

I'm a PG users who has asked our IT team to install pl/perlu on an existing 9.6.0 instance on linux.  They really don't know how to approach this.  Could someone point me to a good step-by-step  (including ptrs to any downloads they may need) ?

 

Also, when they do this, will it require DB downtime ? 

 

Thanks in Advance !