Since 1/8" chains (usually) come with connector links (master links), shortening is straightforward. Generally you use an inexpensive chain tool which you can find just about anywhere.
If you don't have a chain tool, but do have access to a bench grinder, you can grind the pins flush at both ends of the outer link then push them out with a hammer and punch. You only have to push far enough for the plate to fall free, then the link will fall out the other side of the chain. Replace this link with the connector on your bike and you're good to go.
Be sure to measure carefully, because it's a measure twice, cut once kind of a deal. But if you do mess up, you can resplice the chain with a second connector or a chain tool.
__________________
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.