I'm trying to make a homebrewed race that have similar features like the Harengon's "Increase one ability score by 2, and increase a different one by 1, or increase three different scores by 1." and "You are Medium or Small. You choose the size when you select this race." And i'm not exactly sure how to do that. If anyone knows the answer i would be most grateful! 

For them you need to attach Options to the racial traits.

For the ASI trait you will attach 2 Options, one named (+1/+1/+1) and the other named (+2/+1). Attached to each Option you will add the following Modifier:

• Modifier: Bonus->Subtype: Choose an Ability Score->Fixed Value: X

For that second option you want to make sure and make the first X = 2 so it matches the order in the name of the Option to prevent confusion.

For the size trait, make the one option named “Small” and the other named “Medium” and then attach the following modifiers to each Option:

• Modifier: Size->Subtype: [SIZE]
• Modifier: Carrying Capacity->Subtype: [SIZE]

Obviously you want the sizes to both match.

For both sets of traits & Options you can leave all the snippet fields completely blank.

It worked out perfectly! Thank you for the quick reply.

Happy to help.