How do you switch to the sniper rifle attachment?

You got to select assault when the select weapons type appear.

P.S. just check what type of items are on each of the weapons presets.

Hope I helped)

Here's whats up: before you start a mission, you will be given the choise of playing stealth, redding's reccommendation and assault. As you choose one, you will be given different equipment, such as gadgets or attachements. At several missions, you can get the sniper rifle attachment by selecting assault mode (not always, but it says so on your equipment screen). When playing the mission, with your 20-CK equipped, tap the (white)-button to swith attachments.

If all it does is switch back and forth between shotgun and launcher, you don't have the sniper attachment. When you have the choice for Redding's Recommendation, Stealth, or Assault. Scan through them and choose whichever one shows the sniper attachment. Most of the time it will be in the Assault option, but sometimes it is in Redding's Recommendation.
Sniper Attachment is only available on, Penthouse, Hokkaido, Battery, Seoul, and the Bathhouse missions.

This doesn’t help. I’m on the Seoul mission and I PURPOSEFULLY selected assault to give me the sniper attachment. It doesn’t!!! It gives me the shotgun when it clearly said sniper.