How can I get brighter DNA bands?
As you can see from the bottom of the gel, the brightness of the bands have reduced even for the DNA ladder/marker. The main reason for this is that when you are running an agarose gel containing EtBr, due to the positive charge of the EtBr, the stain runs to the negative chamber, against the direction of the DNA migration as @Chris has pointed out! Although some of the DNA will stain but the rest of the EtBr will migrate towards the top of the gel (where the DNA is loaded).

A quick remedy for this is once you ran your gel is to soak your gel in a separate container containing your stain and running buffer such as TAE. I do this for one hour and that makes a huge difference!! Also make sure you regularly change the buffer in your agarose gel running apparatus and don't use the same buffer for a long time since again as @Chris has correctly pointed out there is a reduced conductivity in the older buffers when they heat up so migration does not work as well! Obviously this response assumes that you have a good degree (amount) of DNA in your gel bands, which can be calculated by nanodrop once you extracted the DNA using an extraction kit, or whatever method you normally use. I hope this helps!

This answer is more suited to the title of the question since after reading the main question a bit more carefully I'm slightly confused! So do you see anything at all or your product is far too faint? could you tell us where on the gel, relative to the ladder you expect to see this band? are they the ones at the button of the gel, below the loading buffer?