I believe you want to edit main.lua located in

..\steamapps\common\The Binding of Isaac Rebirth\mods\guaranteed start_1264802784

with a text editor such as Notepad++. Specifically the top of the file:

mod.config = {
-- Config Options Here

-- Set to 'true' to use an item list instead of filtering by quality
useItemList = false,

-- List of items you can find if the feature is on
-- Meant to be customized, default list is taken from racing+'s starting item options
rollableItems = {
CollectibleType.COLLECTIBLE_MOMS_KNIFE,
CollectibleType.COLLECTIBLE_IPECAC,
CollectibleType.COLLECTIBLE_TECH_X,
CollectibleType.COLLECTIBLE_CRICKETS_HEAD,
CollectibleType.COLLECTIBLE_MAGIC_MUSHROOM,
CollectibleType.COLLECTIBLE_DR_FETUS,
CollectibleType.COLLECTIBLE_TECHNOLOGY,
CollectibleType.COLLECTIBLE_POLYPHEMUS,
CollectibleType.COLLECTIBLE_TECH_5,
CollectibleType.COLLECTIBLE_20_20,
CollectibleType.COLLECTIBLE_PROPTOSIS,
CollectibleType.COLLECTIBLE_JUDAS_SHADOW,
CollectibleType.COLLECTIBLE_BRIMSTONE,
CollectibleType.COLLECTIBLE_MAW_OF_THE_VOID,
CollectibleType.COLLECTIBLE_INCUBUS,
CollectibleType.COLLECTIBLE_SACRED_HEART,
CollectibleType.COLLECTIBLE_GODHEAD,
CollectibleType.COLLECTIBLE_CROWN_OF_LIGHT,

CollectibleType.COLLECTIBLE_SAD_ONION,
CollectibleType.COLLECTIBLE_CRICKETS_BODY,
CollectibleType.COLLECTIBLE_MONSTROS_LUNG,
CollectibleType.COLLECTIBLE_DEATHS_TOUCH,
CollectibleType.COLLECTIBLE_DEAD_EYE,
CollectibleType.COLLECTIBLE_APPLE,
CollectibleType.COLLECTIBLE_JACOBS_LADDER,
}
}

aight thanks man

No worries :) Enjoy