From Longman Dictionary of Contemporary Englishtouch somebody/something ↔ up phrasal verb1 IMPROVEto improve something by changing it slightly or adding a little more to it She quickly touched up her lipstick. The photograph had obviously been touched up. The speech he finally gave had been touched up by his staff.2 British English informal to touch someone in a sexual way when they do not want you to He was accused of touching up one of his students. → touch→ See Verb table
Examples from the Corpus
touch up• Perhaps the photographer has touched it up.• This guy sitting behind me started playing with my hair and touching me up.• At home, she wanders around, perpetually touching and picking up things.• We were still climbing at full power and a touch of nose up trim enabled me to increase the rate of climb. 