you can use ESCAPE like given example below
The '_' wild card character is used to match exactly one character, while '%' is used to match zero or more occurrences of any characters. These characters can be escaped in SQL.
SELECT name FROM emp WHERE id LIKE '%/_%' ESCAPE '/';
The same works inside PL/SQL:
if( id like '%/_%' ESCAPE '/' )
This applies only to like patterns, for example in an insert there is no need to escape _ or %, they are used as plain characters anyhow. In arbitrary strings only ' needs to be escaped by ''.