unmounting using disk utility

I wrongly ejected a memory stick from my MacBook Pro... now when I insert the stick my MacBook won't recognise it on the Finder page. I've been to Disk Utility where I can see the stick listed and I've selected it and run first aid. It says it's OK. Now I have to unmount the stick and later re insert it, etc, but I've not an option to unmount - only mount. What should I do next? Any other solutions?