Try hand feeding it, but it should be fine.
My male red betta is a community tank with 19 neon tetras, 5 leopard danios, 6 swordtails and 3 clown loaches, it gets its food no problems.
This betta settled into my tank surprisingly quickly, now taking food from my tank and is doing extremely well.
Some of them are slower than others, they not fast swimmers, try dropping in too at several different spots rather than one, distract your fast fish with a little food and drop some more food in another spot closer to the betta.