I would suggest that you simply wait. You only have 7.
Culling is done by selecting the fish that you do not want and euthanizing them. The easiest method is an overdose of clove oil. I put them in a 1 litere beaker and add in a bit of water that has clove oil shaken into it.
Unless there is a fry with a VERY obvious problem such as a curved back that looks like an "S" or something, you do not need to cull at this time. There is plenty of time to make decisions when they start to grow and you can see them better.
If you are not looking specifically for a "show" fish or a fish with a specific body conformation, all you want is a healthy fish. That is something time will tell.
Many fry go through a " dangerous time" at about 5 weeks, 8 weeks and 10-12 weeks of age when many seem to outgrow their bodies ability to "live" and they die - without warning or anything you can do. Simply waiting until you get them past the first couple of dangerous times is a good idea, too.