How should I clean this lens?

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I'm still pretty new to photography, I current have an Olympus E-M5.1 with a 12-42mm F3.5-5.6 pancake lens on it. Its been pretty fun too shoot with over the last couple of months but when it gets dark i struggle a little to get the shot I want. So I ended up getting a used Olympus 12-40 F2.8 Pro used off eBay. When it arrived I noticed the element on the mount side had a pretty good smudge on it (as shown below). Since I haven't cleaned a lens before and nervous about ruining this really nice investment, what would be the best way to clean that smudge without scratching the glass.

https://preview.redd.it/bx7v617a289e1.jpg?width=5184&format=pjpg&auto=webp&s=5e034f910db2f57d4b3efb5cc9ab072e8c97b810

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Posted: 1 month ago
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