UPDATE od
SET value_exists = 1
FROM LII od
INNER JOIN VPL sl
ON sl.it LIKE '%' + od.value + '%'
WHERE od.tn = 'VPL'
AND od.cn = 'it'
AND od.opr = 9
The LIKE operator used with a wildcard on the left hand side of the search expression makes the join non-SARGable (Google it), which results in a table scan of table VPL. Do you really need the leading %?
For fast, accurate and documented assistance in answering your questions, please read this article.
Understanding and using APPLY, (I) and (II) Paul White
Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden