So for some players their version of the flight does not allow them to swap weapons or equipment with their controls. This is a glitch within some of the downloaded versions of this build, and is rather easy to fix. The glitch itself fails to bind one of the control buttons, so yeah your controller or keyboard works just fine! Follow these steps to fix the error and rebind your buttons/keys. Please heart this if it worked for you.
Step 1: Open Halo Infinite Flight main menu
Step 2: Open game settings
Step 3: Locate controller settings
Step 4: scroll down to “ON FOOT” Section
Step 5: Locate “Switch weapon/Drop equipment”
Step 6: Push “A” Button or click for PC.
Step 7: Press the desired button for switch action
Now get back into the fight Spartans, might wanna swap to that secondary asap, your almost out of ammo!