There’s a simple joint where the tube meets the sprayer (circled above). The tube simply slips into a slightly larger hole at the bottom of the sprayer. What you want to do is switch the tube from the bottle you want to fix onto the sprayer from the bottle that works.
To get the tubes out of the sprayers just pull them firmly out of the joint. It might take a little bit of tugging, but it won’t be too hard to get it out. Then simply take the tube from the bottle you are fixing and push it into the joint of the sprayer that is working. Now you can screw the sprayer on the bottle you are fixing and you should have a fully functioning, albeit possibly weird looking franken-bottle!
So now you made some use of the product you don’t use or already used up, and you don’t have to stop using the product you love! Or annoyingly have to go out and buy a new one.
If you really can’t find a sprayer that fits you can always try pouring the product into an empty bottle, but I don’t like risking the spillage, and sometimes there isn’t enough room in the new bottle and you don’t realize until you already poured half of it in and then you are really screwed. It can get messy. Same goes for a travel bottles.
The point is just don’t throw it out! Wasting things sucks. My grandma really drove home the whole “waste not want not” thing and it stuck. You can make it work, just channel your inner MacGyver and get a little creative.