Remove jagged obstacles like DW. If there are floating plants put into bucket.
Don't feed for a day. You might need to remove the Betta for a day to keep from getting nipped from hungry Ember Tetras.
Use an appropriate sized net (black seems to be least noticed with my zillion guppies /Endlers) at least 3-4 times the size of fish. 4" is fine.
I try and be positioned more under and at a 45 degree angle and scoop up. say feed towards the right side of the tank, position in the low center and swoop right and up.
Also when you start - feed just add a few bits of the food to get their attention. Wait to get to them towards the location you want. Often you can swoop up a bunch right before they know what happens.
Option one is patience, and stop at the first scoop - don't chase.
With hoping you have a few, then wait an hour and do the same thing.
The other option which works well is an extra person (but you can do it by yourself) to shoo them towards your net, and swoop up. This is best for when they are onto you and hide when you walk into the room, lol!
Other possibilities is lower water and wait for the fish to go to one corner and scoop.
Another thing is to try and know for sure how many fish you have exactly so you can breathe a sigh of relief after getting them all!
It could take a few days to get them all. I have had to remove the majority of plants and DW and stones to capture fish. But lately I have been getting better at it since there are so many Guppies /Endlers, and fish I have changed around from one tank to the other.
Also you go gently against the glass - you can squash the little guys with a too vigorous attempt.
Making sure the net is squared, otherwise there is sideways escapes.
And there are no holes in the net, lol, all experiential advice!