Stiff Chain Link

[OakLeaf]

I would just replace the chain. There's a reason the link got stiff, and if there's abnormal wear in the one link it's likely to be pervasive. It's not as huge a deal as it is on a motorcycle, but if your chain breaks, you'll either need to put it back together or you're stranded. Meanwhile, your sticky link is damaging your chainrings and rear cogs.

Basically, assuming a good initial installation, the reason links get stiff is lubrication washing out, wear and rust.

You'll need a chain tool to remove the old chain even if you get a new one that installs with a master link, so either get a chain tool and learn to use it, or take it to your local bike shop.