I am making a magical item that would allow the user to go beyond the normal 20 cap in this case a wizard with a 20 intelligence would be able to raise it to a 24 intelligence. 

Q. Is there a way to do that when making a item in homebrew working similar to the belts of giant strength 

I suppose the first question is this - how do you want the item to do this?

1. Set their intelligence to a fixed value? (In this case 24) - Yes, this can be done quite easily. Just create a copy of a Belt of Giant Strength and modify it to affect Intelligence instead of Strength.
2. Add a generic amount to their intelligence? (e.g. it just adds a flat 4 to whatever they have?) - (edited) yes, just add the options specified by sigvard_vigrid below
3. Allow them to do it via ASI? - (emitted) Actually, yes. If you increase the max stat as suggested below then you can apparently spend ASIs on it just fine.

When you create the item, you need 2 modifiers. 

Modifier type: Bonus

Modifier subtype: Intelligence score

Fixed value: 4

--Also--

Modifier type: Bonus

Modifier subtype: Ability score maximum

Ability score: INT

Fixed value: 4

Use both if the item gives a +4 and raises the max to 24. Only use the second if the item just increases the max to 24.

Quote from Sigvard_Vigrid >>

When you create the item, you need 2 modifiers. 

Modifier type: Bonus

Modifier subtype: Intelligence score

Fixed value: 4

--Also--

Modifier type: Bonus

Modifier subtype: Ability score maximum

Ability score: INT

Fixed value: 4

Ah, that’s what I’d forgotten. I was sure I’d seen that when looking through stuff but couldn’t see it again when I was fiddling with an item as a test.

Got it from the manuals/tomes that give a bump and increase the max. 

Edited my earlier answer for clarity. All 3 are actually possible. Which is handy