I don’t know if this is okay to ask here but what is a good agent to get a tourist visa for South Korea?

I've got a friend who is from South Korea. After receiving a 90 day Visa. They were advised at the Immigration office they were only able to extend for 7 more days. They did this, and now, they would like to renew for another 90 (or at least 30 days). If they do a border run to Myanmar, will this allow them to renew their VISA??

Thanks for your help!

Advice needed

My niece is visiting Chiang mai first week of January, flying from New zealand using a NZ passport

Wanting to stay 4-5 months, however after the first two months she plans to fly over to S Korea for one month then return to CM for 2 months.

She is my niece,17 years old

What is the best visa approach?