Probably you've flashed some boot USB or ISO image which have size of only ~49MB. That process clears the flash drive's MBR and replaces it with the one in the image that contains a small partition. You can verify that by opening
diskmgmt.msc and check if there is only a single 49MB partition
If that's correct then just delete and recreate the partition. Or use some 3rd party partitioning tools like gparted, or EaseUS® Partition Master or MiniTool® Partition Wizard Home Edition to extend/recreate the partition
Another GUI solution is Rufus
So, you created a bootable drive, possibly with a DD image, and now Windows no longer seems to see it, or it reports that its capacity is much smaller than it actually is. And now you want to "restore" it to a state where you could just use it to copy files, with Windows recognizing the drive and letting you use its full capacity.
Well, what you really want to do is "restore" your drive to non-bootable state. And, of course Rufus has a very prominent way to allow you to do that.
See the Boot selection dropdown in Rufus? The one that has a Non bootable entry? Well, if you select that option, and then pick whatever you want for the file system, then Rufus will happily "restore" your media to something Windows will recognize, with full capacity, and that you can use again to transfer files. That's all there is to it.
If you don't want to use GUI then there's the built-in
diskpart that you can read about its usage in the other question